F' L R' U //EO
F' R F R' //4c4 in 8
(R2 F^ L2 B) D2 L2 B' D2 B'^ //HTR in 17
R2 D2 B2 D2 //slice in 21
^=w

Super simple solve. You have to solve 4c4 but the optimal solution is exactly of the form you should be looking at first:
Shortest possible reduction to 4b2 2e (on inverse in this case) and then NISS.

U (L' R' U) //EO
(R) R' F L2 B' R //2c4 in 10
U2 B'^ (B'^ L2 U2 B' D2 B) //HTR in 18
(L2 D2 F2 R2 D2) //slice in 23
^=w //+0 

(L' U' B) //EO
(U' R) U' D2 R' D R //2c3 4e in 10
(L2 D' B2 [D R2 U') //HTR in 16
(L2 B2 U2] F2 B2) //slice in 21
[]= Dw R2 U' L2 B2 U Uw //+1/22

I'm kind of losing motivation for FMC lately :/

U D' L' D //EO
R (B2 R2 B D2 L) //2c4  10/23
(B' R2 F D2 L2 F D2 F') //HTR 18/23
(L2 D2 F2 D2 U2) //slice 5/23
widen everything //+0/23

I wrote down 11 different sub12 DRs and every single one was 4 or 5 qt :D

(R2 B U') //EO 3/3
F' //jzp 1/4
(R2 F D2 {F' L2 B) //4b2 4e 6/10 with 3qts of jzp to work with!
R U2 D2 [R2 U2 B2 L' //HTR 7/17
B2 L2] U2 {B2 //double slice 4-1/20
[]= L2 D2 F2 L' F2 R2 //slice +0/20
{} = Bw L2 Fw //+0/20

NICE!
This was the only DR I looked at. I also tried to solve few other double slices from this.

(D) B U 3/3
F L R' , B R' F R' //2c3 2e 7/10 Cursed DR line :D
D2 B^ (B'^ D2 B) //HTR 5/15
U2 R2 F2^ U2 R2 U2 R2 //slice 7/22
^=w //+0/22

DR is 21 opt but with 5qt :D

Also had:
U (F2 D) ( U2 F U2 R' F' L) //9 move DR but 4b5...

U L2 F R L (U' L2 U' L2 U' F) //2c3 4e in 11 but ending in F R L so potential. But there is nothing great. Best findable is 23 and optimal is 22 again with 5qt.

F L U //3/3
(B2 R U2 L2 B R2 B) //2c3 6e 7/10
R^ B2 U2 F2 U2 R D2 R'^ //8/18
F2 R2 D2 B2 D2 B2 //6-1/23
^=w //+0

Also had:
F L U, R, D2 B L2 D2 B L //4a2 4e in 10 but cursed since corners are all in same layer on both sides. 24opt.
F L U', F, R' B2 R2 F2 L' F //2c4 in 10 easy linear 23opt.
D2 F L U B R2 F2 L U2 B2 L //2c3 4e in 11 with variations and this one is +5 to HTR. Also 23opt.
Edit: I am an idiot. There is a 10 move 2c3 4e from here and it has an easy 22....

R' (R') //EO 2/2
U F' , R2 D2 R2 U' B' //4a2 2e 7/9
L2 U (F2 R2 L2 D') //HTR 6/15
F2 U2 //pseudo FR 2/17
F2 L2 B2 R2 F2 U2 //solve 6-1/22

Also had:
R (R)
F B , D' F U2 B //0c3 in 8 that is 21 opt but missed it.

Also the R2 U2 L2 U' F variation of the 4a2 2e is 21 opt but it is NISS HTR with M U2 M U2 type insertion to HTR so I missed that HTR.
nissy-# solve -o -t 64 R' U' F D B' D B2 R' U2 L R B2 R B2 F' L U' F' L2 F' D2 U2 R' U' F R' U F' R2 U2 L2 U'
B D2 F' B U R2 U2 F2 L2 F2 R2 U F2 R' (14)

D' L' F' U //EO+rzp 4c6e 4/4
R2 F' R2 B2 R^ B2 L^ //4a1 4e with variations and double slice potential 7/11
([F2 R2 D2 L2 F']) //HTR 5/16
(U2) //double slice 1/17
^=w //slice +0/17
[]=Fw2 R2 F Fw' D2 L2 Fw' //+2/19

Nice!

(U2 R2 B2) //EO 3/3
(U' L') F2 U L2 D' [R //4a2 4e 7/10
(R2 U B2 U2 F2 R2 D) //HTR 7/17
(B2 D2 [B2 L2) //double slice 4/21
[]= (R' L U2 L) //slice +1/22
Widen all U/D turns post-DR for +0/22

B D L U F' //EO+rzp 5/5
D U2 F2 R //4a2 2e 4/9 (There is also D' B2 L for 4a2 4e in 8 that I spent a lot of time on but that is absolutely horrible...)
(R2 D) F2 U B2 U2 L2 U' L2 U //HTR 10/19
F2 L2 U2 L2 D2 //solved 5-1/23

This 8 move DR is insane bait! There is one unfidable 14 and insanely hard 15s from that. 
And this extension to 9 also sucks.

I also tried extending to 
F2 R2 F2 D' B2 L //4a2 4e in 10 but no luck there either...

Got way too stuck on this and didn't therefore have any other good DRs...

(B' U' F') //EO 3/3
(U]) D2 L D2 F2 L' D //4b2 2e 7/10
{L2 B2 L' D2 L} //HTR 5/15
F2 [U2 F2 U2 //double slice 4-1/18
[]= U D R2 D U2 //slice +2/20
{}= Lw2 B2 Lw L2 D2 Lw //+1/21

Optimal from all DRs I looked at.

Had so many promising DRs this attempt including:
(B U' F , L2 U) U2 L2 F2 L R2 D //4a1 4e in 11, 23opt
(B U' F' , R2 D) F2 B2 D2 L R2 D //4a1 4e in 11, 23opt
(D2 B' U' F') (R' F2 L' R2 U) //0c3 in 9, 24opt :D

And then a bunch of decent subsets in 11 or 2c4 in 10.

This ties cubelib with my settings!

R (F B2 R') //EO 4/4
(D) (L2 U2 F' B2 D) //2c3 4e 6/10
B (F'^ U2 F^ R2 F R2 F) //HTR with 5qt :D 8/18
(R L' U2 L R') //slice 5/23
^=w //+0/23

L' B D2 R //EO+rzp 4/4
F2 D L2 U2 B2 D' B' //4a1 4e 7/11
D^ R2 U^ B2 L2 B2 U' //HTR 7/18
F2 D2 R2 B2 L2 //slice 5/23
^=w //+0/23

DR opt.

Also had:
L' B D2 R' , B2 D' L2 U2 F2 D F //4a1 4e in 11, variation of final DR. Also 23 opt.
L' D' B R , U , L2 B D' F D //4b2 4e in 10. 24 opt.

Kind of bad luck that 23 is overall optimal from those 3 DRs... But that is FMC for you.

B' U2 D' F //EO+rzp 4/4
L2 U2 L2 U' R' U' //2c3 2e 6/10
R (U2 L2 F2 L B2 U2 L) //HTR 8/18
(B2 L2 ^ D2 F2 ^ R2) //slice 5-1/22
^=M2 //+1/23
DR is 22 opt but 3 HTs before trigger so not that bad of a miss.

Also spent time on:
B' U2 D' F , L2 F2 U2 L2 U' R //4a2 4e in 10. 23opt.

(L) U F' R //EO 4/4
F , D R2 D F2 U D' B //4b2 2e 8/12
U2 F2 B2 U^ R2 D^ //HTR 6/18 
R2 F2 R2 D2 B2 L2 //slice 6-1/23
^=w //+0/23
Backup I found early.

Also had:
(D') F' L U (F' R2 F R' F L) //4c3 in 10. 22 opt but needs 2 HT before first qt so didnt find it.
And then million 2c4 from the 3 move EOs. So probably also like 22 in there but no way I can check all of those.

L' (D' B2 R) //EO 4/4
(D) F' L2 F B2 U' //2c4 6/10
B (B' D2 B L2 U2 F) HTR 7/17
(R2 * U2 F2 D2 B2) //wrong slice 5-1/21
*= R2 F2 R2 U2 L2 B2 L2 U2 //solved 8-5/24
But now after DR we have:
(B' D2 B L2 U2 F' R2 U2 L2 [B2 L2 F2 D2] B')
[] is just a blocky fish! So:
[] = U2 F2 R2 B2 //slice -1/23
and widen 1st and last qt for //+0/23

B D R' D //EO+rzp 4/4
F U2 R2 B2 F' R //4a1 4e 6/10
(U2 B L2 U2 L2 [B' D2 B') //HTR 8/18
(R2 U2 D2 L2]) //slice 4/22
[]= F' R2 F' L2 U2 D2 R2 //-1/21

Other:
D (F' D) L U2 L2 R F //4c4 in 8. Also 21 opt but didnt find that
B' D R' D , B' U2 F R2 F' R //4b2 4e in 10. 23 opt.