?

a) 24/23 is very attractive, providing insurance against gammons.
However its pasivity surrenders too many winning chances.  O is
already very advanced, so X needs to try and send a man back.

The first ace is forced.  Then, making the five point seemed automatic
with the decision being whether to hit from the midpoint or make the
anchor.  A systematic flaw in my play is to attack even when defense is
called for, and I hit here: bar/24 13/12* 6/5(2).

But facing 12 checkers in the zone and a solid 5-prime, and with no
board of my own,  anchoring up is a must.  Hitting is a double whopper
with cheese.

Once you see that anchoring is mandatory, making the 5 is an easy choice.

XGID=------EbCB--aCaa--bbbbbA-A:1:1:1:11:0:0:0:5:10

X:Player 1   O:Player 2
Score is X:0 O:0 5 pt.(s) match.
 +13-14-15-16-17-18------19-20-21-22-23-24-+
 | X  O  O        O |   | O  O  O  O  X    |
 | X              O |   | O  O  O  O       |
 | X                |   |                  |
 |                  |   |                  |
 |                  | X |                  |
 |                  |BAR|                  |
 |                  |   | X                |
 |                  |   | X                |
 |             X    |   | X                | +---+
 |          X  X  O |   | X                | | 2 |
 | O        X  X  O |   | X                | +---+
 +12-11-10--9--8--7-------6--5--4--3--2--1-+
Pip count  X: 159  O: 120 X-O: 0-0/5
Cube: 2, X own cube
X to play 11

    1. Rollout¹    Bar/23 6/5(2)                eq:-0.378
      Player:   31.32% (G:4.89% B:0.26%)
      Opponent: 68.68% (G:15.25% B:0.89%)
      Confidence: ±0.008 (-0.386..-0.370) - [100.0%]
      Duration: 14 minutes 24 seconds

    2. Rollout¹    Bar/23 6/4                   eq:-0.493 (-0.115)
      Player:   27.48% (G:4.23% B:0.25%)
      Opponent: 72.52% (G:15.84% B:0.69%)
      Confidence: ±0.008 (-0.502..-0.485) - [0.0%]
      Duration: 14 minutes 20 seconds

    3. Rollout¹    Bar/23 13/12* 12/11          eq:-0.603 (-0.225)
      Player:   25.26% (G:3.87% B:0.19%)
      Opponent: 74.74% (G:19.62% B:1.10%)
      Confidence: ±0.009 (-0.612..-0.594) - [0.0%]
      Duration: 16 minutes 25 seconds

    4. Rollout¹    Bar/23 13/12* 6/5            eq:-0.630 (-0.252)
      Player:   26.72% (G:4.22% B:0.21%)
      Opponent: 73.28% (G:24.90% B:1.63%)
      Confidence: ±0.009 (-0.639..-0.621) - [0.0%]
      Duration: 17 minutes 10 seconds

    5. Rollout¹    Bar/24 13/12* 6/5(2)         eq:-0.654 (-0.276)
      Player:   29.17% (G:6.53% B:0.42%)
      Opponent: 70.83% (G:32.69% B:2.03%)
      Confidence: ±0.010 (-0.664..-0.644) - [0.0%]
      Duration: 14 minutes 45 seconds

¹  1296 Games rolled with Variance Reduction.
   Moves: 3-ply, cube decisions: XG Roller

eXtreme Gammon Version: 2.03, MET: Kazaross XG2

My sense is that the right way to think about bar/23 is not so much
"anchoring" as "stepping up to the edge of the prime."

One way to partially test this theory is, change the position by
moving X's 23pt blot to the 24pt.  Then bar/24 already "anchors" but
doesn't step up to the edge of the prime.  How do the plays rank now?

I'll post your variant as another quiz, and make my comments there
before looking at the bot's answer.