Nice problem! Blue loses more gammons than I expected by staying back, making this a trickier problem than I expected. At DMP, it is clear to stay back in all your variants, but look for example at what happens in your original position if we change the score to 4a5a:
           
 
         
 | | White is Player 2
score: 0
pip: 101 | | 5 point match | pip: 145
score: 1
Blue is Player 1 |
|
| XGID=----BBCAB---bB---cBec-b-A-:0:0:1:61:1:0:0:5:4 |
| Blue to play 61 |
| 1. | XG Roller++ | 24/18 6/5 | eq: -0.728 |
| Player:
Opponent: | 25.32% (G:1.81% B:0.02%)
74.68% (G:4.20% B:0.05%) | |
|
| 2. | XG Roller++ | 24/18 8/7 | eq: -0.733 (-0.005) |
| Player:
Opponent: | 25.21% (G:1.83% B:0.02%)
74.79% (G:4.11% B:0.05%) | |
|
| 3. | XG Roller++ | 13/7 6/5 | eq: -0.770 (-0.042) |
| Player:
Opponent: | 32.33% (G:4.55% B:0.13%)
67.67% (G:19.55% B:0.28%) | |
|
eXtreme Gammon Version: 2.10, MET: Kazaross XG2