Michael - thanks for that. It makes sense with thick cold oil and the narrow dipstick tube. My practical experience taught me that as well. I leave it dipped for about 20 seconds now rather than 10 before I read it. I'm a few hundred miles away from mky next oil change. I'm planning to have the pan dropped and the pressure relief valve serviced then. I also suspect that the synthetic oil used for my last oil change was 0W40 (dealer fill from oil supply for new cars) rather than 15W50. I'm thinking that may be part of the reason for my recently-reduced idle oil pressure.
1995 E320 Wagon Moonstone Grey/Parchment 106K mi.
2007 E63 AMG Graphite/designo 75K mi