White likes to hit, but has to choose between the blots on the 22 point and on the 11 point. If he hits the blot on the 22 point, then the blot on the 11 point is much easier to safe relative to the blot on the 22 point. After hitting on the 11 point, the blot on the 22 point can only be covered by shifting the problem to the 17 or 18 point.
Don't feel bad. Most players would get this wrong over the board, me included. But here's what's happening.
Black is stripped on his 6, 7, 8, 10, 12, and 22-points. If you play Bar/24 13/11* Black has a lot of entering numbers which make him break one of his outfield/blocking points. Those variations are very good for you. If you play Bar/22*, he can use his outfield spare to play all those awkward entering numbers without breaking any vital point. Very tough problem over the board, not so hard once you know the answer.