That is really interesting, try this a couple times with the 5w30 redline and see if you still have to do this. As in don't adjust, just try what makes it tick with 5w20 and see if it still happens. The drain back valves don't work, oil is hot when you turn off your truck and there is zero chance that valve holds back thin oil under gravity. However, most hemi's when they park are level and due to filter location it holds oil at least in the filter. My guess your situation oil is not only not being held in lines, but actually draining from the filter as well. I really am curious if the 5w30 will help you here, if it will have more oil or film stay on the metal when you turn it off hot. I think common oil knowledge will say it isnt gonna happen, but if nothing else we have proven common oil knowledge have some holes in it
If you ever do a relocate filter, you might want to tip the unit to match the parking angle if this is a permanant situation. But then it will be an issue when level, but I would want the first cold start protected more as opposed to when you drive to the store. Hella interesting case, just maybe 5w30 redline will work. I would never suggest the 10-48, but like I said interesting case, maybe this would work, dunno. The issue with the 10-48 is warm oil idle psi, but at the moment this isnt the issue. Then what if 10-48 works on start up and the 10-48 also keeps warm idle tick away. The fact is, it is good you are taking steps and trying stuff, these engines let you know when they arent happy, and with cam/lifter issues being so prevalent, it sounds like maybe you are close to the sweet spot. Just maybe 5w30 solves everything, if so stay with bigger filter imo.