oil pressure at idle

[b_rad]

In my 91 TT I have the stock oil pressure gauge. it has 108k miles but the thing is i feel like my pressure is really low considering my 93 NA sits at about 1/3 the way on the gauge (maybe the 4th hash mark). sometimes the gauge on my 91 TT will read even lower (only 1 hash mark from the bottom) after driving it and letting it idle once i park. most of the time it will sit no higher than the 2nd hash mark while idle.

i attached a picture. my question is where should my idle pressure be at? it has no problem while driving and the pressure rises normally as it should while driving.