If it is uneven, it will push on the uneven parts. Tank manufacturers will void the warranty if you put foam under their glass tank. Make sure your stand is level, and you won't have any problems. The only support a glass tank needs is around the edge of it. I don't know why one would even consider putting foam under one. It seems like someone thought it would be good idea, and for some reason others have done it. Why would it need a cushion? Makes no sense to me.
The manufacturers of my 180 gave a warranty on the tank on the proviso that the SUPPLIED foam was used as a base between tank and stand. Every tank I have ever bought that didnt have a floating bottom was sold with the instruction to put foam underneath
