the min oil pressure for an s2 when hot is 14.5 psi from the book give or take a bit, the oil light doesent come on until between 4.3 to 7.2 psi so you have a fair bit of a margin there 13psi is quite ok for hot oil at idle and dont forget gauge accuracy
the main thing is you have good oil pressure under load which should be around
40 psi at 2000 rpm
the oil pressure relief opens at 58 psi so unless its jammed closed you wont get any more than that.