BP FL Order of Difficulty?

I'm using the BP FLs (1-4) before switching to AAMC FLs. I'm curious if there is a consensus on how difficult the BP FLs are compared to each other like there is for the AAMC FLs.

I know people say BP is harder overall so not to interpret too much from a score, but I'd like to be able to track progress accurately from exam to exam.