The 30-40 foot discrepancy is not a meme and it most certainly didn't start on social media. It came from (a) Zimmerman's own statements to SPD as to where the altercation started and how it unfolded as compared to where the body and shell casing were found, plus (b) measurements taken from a sketch of the crime scene. In other words, it's based on actual evidence from the trial.
Zimmerman gave no less than half a dozen separate statements to SPD, including his written statement from the night of the shooting; interviews with Detectives Serino and/or Singleton on 2/26/12, 2/27/12, and 2/29/12; a voice stress test; and the reenactment.
In all but one of these statements, he says he was punched and at the "T", fell backwards and was mounted - making no mention having somehow moved 30-40 feet down the sidewalk. Only in the one reenactment video does he mention stumbling, and even then he never says it was as far down the sidewalk as where the body was found. In other words, even if we take his explanation from the reenactment as true, there is still a discrepancy of another 20 feet or more that remains unexplained.
I guess we'll have to agree to disagree because I'm just not convinced by an unsatisfying half-explanation that (even if true) still leaves a material discrepancy, and that only appears in 1 out of 6 of his statements. I think the simpler and more likely explanation is that Zimmerman lied.