I run my pretreated garments through a belt drier, then heat press them around 20-30 PSI to keep the pressure lines minimal and flatten the fibers. Assuming you don't have a belt drier, you can probably keep the PSI that low and extend the amount of time you heat press it to dry the pretreat.
That being said I have heat pressed pretreated garments at 60 PSI and that still works fine but the pressure lines are noticeable.
I like to use a belt drier for curing the garments, and then I will heat tap the garments for 5 seconds with a low PSI (around 10) for high profile samples to give it a better feel.
I wouldn't go over 20 PSI when you are curing the ink.