You touched on the problem, a contributing factor, then went sideways.
There is no influence from the factory relief valve at idle unless it is stuck open then you have bigger issues. There is enough internal leakage, by the oil pump gears and internal clearances/orifices, to prevent adequate pressure to crack the relief valve. They start to crack and about 28# and fully open at 32#, YMMV. A cheap Baisley spool valve improves the seal of those but these days they don't seem to be the chronic issue they once were. The cams intensity of the ramps is another contributor. Hydraulic Intensity is the difference between the . 004 duration and the . 050 duration. The stock 255 cam has fast ramps. Then last but not least pushrods that flex under the added pressure. Valve springs don't help either. The flat damper dual springs do not adequately control the problem, but I would consider these lower on the scale of what hammers lifters and causes early failure. The springs weight is a contributor. The myth is the springs have too much pressure, not true.
The springs do not control a valve train with heavy valves, heavy springs, pogo stick pole vault pushrods, and a cam that has very steep ramps. Oil pressure is adequate to refill the lifters but true that low speed pressure raised would not hurt anything. That takes a closer tolerance pump and < .003 crank runout for that pump to live.