The thought on the amount of curd was the "sponginess" of the curd. The more curd the more resistance to a fixed PSI.
So, for example. Take an 8" mould that is 1" deep in curd and an 8" mould that is 60" inches deep in curd. (a bit rediculous, I know) In order to properly press the center of the longer cheese mould, would you still use the same PSI? It seems to me that the deeper cheddar might push back a bit more (and thus need more PSI) than the 1" deep mould.
Its a bit academic, in that i will never do this, its just a thought experiment.