After the best play (shown below) blue has quite an issue with any roll that doesn't hit and cover or is a playable doublet. He can't hit with non natural fives so those numbers don't concern us in the original problem. Hitting with other fives like [65 or 51] we're indifferent to leaving essentially only the hitting + covering fives and [55] as decent rolls. With other rolls, as you mentioned, now the midpoint is frozen as leaving a shot is out of the question so blue will have to trash up his position even more with most numbers containing a large die. (race is close so wasting pips is not desirable obv)
As you also mentioned, leaving our straggler in the opp's inner board is too far from freedom and doesn't restrict the opp's position.
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