Neil's answer is complete. But, I think the main point is so obvious to him that he didn't emphasize it as much as he could have done. You do not need to contain the checkers on the ace. They aren't going anywhwere unless he rolls 66. Contact favors your opponent. You are happy to let him break contact. By making the bar, you just risk leaving a six shot when you eventually clear it. The one advantage of making the bar point is that it prevents leaving fly shots from the ace if you have to leave an outfield shot. Otherwise, it is a liability.
Check a similar position (below). Improve your position by making the deuce point. Now check the best way to play 11. If making the bar is still wrong or close, it should be easy to understand that it is wrong by a lot in the original position.
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is Player 2eXtreme Gammon Version: 1.21