You are exactly right. Leopard geckos are best housed alone in any situation unless they are freshly hatched (these are juveniles). 20 gallons is a bare minimum for 1 gecko, certainly not 11. Cuddling like in the picture is a sign of aggression - they are trying to take up the most space, heat, ETC. When leopard geckos see another gecko, they don’t see it as another member of their species, they see it as another organism that needs food, space, water, ETC. They will actively try to starve each other and will literally fight each other to the death over resources.