Is there any way to explain the best play here? The best play involves abandoning the hope to anchor on 21pt.

You are behind in the race. You have 3 men back. He has one. Equal board strength. This is crying for some contact semi-bold play. His game plan is to run home safely (and he seems to be going pretty well at it), so yours should be to make things harder for him.

21/16 13/9 seems to support your game plan pretty good considering the awkard roll. You invite a hit contest and make something constructive on your side of the board too.