Yes, elite wave technically is supposed to be in front of corral A, but in my 2 WDW marathon experiences, there was no real separation. In 2017, I think I was about 5 rows from the line--I knew what kind of time would win it, so no need to push up to the very front--that wasn't going to be me! I looked at those results and I crossed over the start in 1 second (finished 9th OA, 3:07). In 2019 I had an elite bib again. I decided to run this easy and make character stops (I think I hit 12 of them). I didn't care where I started and think I was in the mid-back of corral A. Looking at results, it took me about 16 seconds to get across the start line (finished 22nd OA, 3:22).
Really, if you are in A, crowds aren't going to be an issue. I am not sure what time gets you an elite bib--both times I submitted a sub 3 hour marathon. Any other marathon, it would not be elite.