I do not believe it is recommended that BPs eat prey that is wider than the widest part of their body. What I have usually seen is that it should be about equal to the widest part of their body. I have seen up to 1.5x times as wide recommended for other types of snakes, such as corns.
Also, I believe both that rule and the 10-15% rule apply to young, growing snakes. Once they reach a certain size, you can stop increasing the size of the prey even though the snake will continue to grow slowly.