When cold,your
oil pressure will always be higher than fully warmed up
oil....after your 30 minute ride, your
oil temp should be in the 180 to 200 degree range,hot and thinned out,so it flows better than cold/thick oil,hence the lower oil pressure.........
20 psi with hot oil at idle is fine..........
As long as your oil pressure comes up with rpms,say to at least 40 psi or more, I wouldn't worry about it........
david