I've not seen the aerial shots but have you considered a fair number may have already been inside?
30k+ sounds like a lot of people chancing their arm and I agree that it's probably on the high side, but remember there were estimates of between 50k and 150k Liverpool fans being in Paris. Let's take that middle figure and call it 100,000. 20,000 had legitimate tickets which leaves 80,000. Let's assume that several thousand also managed to get hold of tickets from the neutral allocation. I'll generously round that up to 10,000 making 30,000 Liverpool in the stadium. That now leaves 70,000. The Liverpool fan park held 44,000. Let's assume that was full to capacity for the match itself even though it may well not have been. That now leaves 26,000. Where did those 26,000 go?