Others have very poor off-contact adjustments that really do little than raise the screen from the back. On these presses you need to first raise up the back clamp so the screen sits just above the shirtboard. This usually requires loosening the bolts and manually lifting the back clamp. The shim does not mean the press is not made good. It is impossible to hold the screen off contact when the press just has a rear clamp.
Automatic presses hold the screens off-contact because they hold the screen on both ends.
This is impossible on a manual press. Check the registration bolts This is a pet peeve of mine and one that I was guilty of NOT doing on a recent job. This slop caused the print on that station to be out of register. This movement put a shadow on the bottom of the screens that made the rest of the prints seems soft. Since many popular presses use nylon bolts as the registration guide, simply bring down an arm at each station and try to move it back and forth.