Did the pressure ever get to the 12 or 13 psi you want? Was it lower when the equipment was new? If not, you may never get there. My pressure runs around 20 when everything is clean and new. The normal operating pressure depends on the pump size, filter state, pipe size and length of run, number and size of return openings, etc.

You could try using a larger size return fitting if available (go from a 1/2" opening to a 1", for examaple) if you really need the pressure to be lower and everything else about the system is okay.

You didn't say what kind of filter you have so this may or may not apply. I have a DE filter. When the pool was new and I was going through the initial plaster curing/brushing the pressure went up to 30. I tried backflushing it several times but it only lowered the pressure (to 20) for a day or so then it would climb back to 30. I ended up disassembling the filter and repalceing the DE powder to correct. The old DE powder was cacked with plaster dust and backwashing would not clear it. With new powder in place I'm on the 4th or 5th month without needing to clean or backflush.