I always suffer from this little 21. Today I compare three positions to see the difference. The only difference between problems are Blue's inner board. I wonder why the best play changes as Blue shift the point.
  White is Player 2
score: 0 pip: 152  Unlimited Game Jacoby Beaver  pip: 168 score: 0
Blue is Player 1  
XGID=aBDCaeCbdbBA:0:0:1:21:0:0:3:0:10 
Blue to play 21 
1.  XG Roller++  Bar/22  eq: 0.332 
 Player: Opponent:  41.55% (G:11.03% B:0.33%) 58.45% (G:16.12% B:1.04%)  

2.  XG Roller++  Bar/23 6/5  eq: 0.347 (0.015) 
 Player: Opponent:  42.42% (G:11.33% B:0.41%) 57.58% (G:19.44% B:1.59%)  

3.  XG Roller++  Bar/23 24/23  eq: 0.358 (0.027) 
 Player: Opponent:  40.81% (G:10.94% B:0.33%) 59.19% (G:15.86% B:0.84%)  

4.  XG Roller+  Bar/23 8/7  eq: 0.400 (0.068) 
 Player: Opponent:  40.64% (G:10.90% B:0.39%) 59.36% (G:18.95% B:1.44%)  

5.  2ply  Bar/24 6/4  eq: 0.428 (0.096) 
 Player: Opponent:  38.57% (G:10.31% B:0.43%) 61.43% (G:19.20% B:1.45%)  

eXtreme Gammon Version: 2.10
  White is Player 2
score: 0 pip: 152  Unlimited Game Jacoby Beaver  pip: 166 score: 0
Blue is Player 1  
XGID=aBDCaeCbdbBA:0:0:1:21:0:0:3:0:10 
Blue to play 21 
1.  XG Roller++  Bar/23 24/23  eq: 0.394 
 Player: Opponent:  39.84% (G:10.91% B:0.33%) 60.16% (G:16.76% B:0.90%)  

2.  XG Roller++  Bar/22  eq: 0.428 (0.034) 
 Player: Opponent:  39.40% (G:10.58% B:0.35%) 60.60% (G:17.87% B:1.23%)  

3.  4ply  Bar/23 6/5  eq: 0.412 (0.018) 
 Player: Opponent:  40.09% (G:10.57% B:0.37%) 59.91% (G:19.17% B:1.52%)  

4.  4ply  Bar/23 8/7  eq: 0.471 (0.077) 
 Player: Opponent:  38.58% (G:10.34% B:0.35%) 61.42% (G:19.70% B:1.59%)  

5.  3ply  Bar/24 6/4  eq: 0.549 (0.155) 
 Player: Opponent:  36.93% (G:10.02% B:0.40%) 63.07% (G:21.54% B:1.92%)  

eXtreme Gammon Version: 2.10
  White is Player 2
score: 0 pip: 152  Unlimited Game Jacoby Beaver  pip: 164 score: 0
Blue is Player 1  
XGID=aBDCaeCbdbBA:0:0:1:21:0:0:3:0:10 
Blue to play 21 
1.  XG Roller++  Bar/22  eq: 0.481 
 Player: Opponent:  37.70% (G:10.34% B:0.34%) 62.30% (G:17.89% B:1.19%)  

2.  XG Roller++  Bar/23 24/23  eq: 0.498 (0.017) 
 Player: Opponent:  37.20% (G:10.16% B:0.29%) 62.80% (G:17.33% B:0.94%)  

3.  3ply  Bar/23 6/5  eq: 0.527 (0.046) 
 Player: Opponent:  37.46% (G:10.01% B:0.40%) 62.54% (G:20.65% B:1.72%)  

4.  3ply  Bar/23 8/7  eq: 0.558 (0.077) 
 Player: Opponent:  36.40% (G:10.07% B:0.35%) 63.60% (G:20.59% B:1.73%)  

5.  2ply  Bar/24 8/6  eq: 0.643 (0.161) 
 Player: Opponent:  34.40% (G:9.41% B:0.34%) 65.60% (G:21.18% B:1.63%)  

eXtreme Gammon Version: 2.10