Yo
Thats true. If you want a thicker layer you do a "second pass".
In order to achieve that, you need to have a flash cure. After the first pass you need to gel the layer of ink with the flash (use hair dryer if you don't have it).
Once the plastisol has been slightly dried (approx 110 degree c) make another pass.
You have to have a decent press that enable you to heat your screen on the same spot every time in order to make the print look registered.
Hope that helped.