I'd only keep messing if the current consumption makes it necessary to add oil before the OCI... IOW, if it's consuming a quart every 2500 miles, and OCI is say 7500, then that would be 3 quarts and likely needs a top-off. If the oil still measures in the "safe" range on the dipstick for the duration of the OCI, why bother?
I can tell you from experience on a boxer motors (EJ251, EJ253) that NOACK is not the end-all, be-all of eliminating consumption. My current Outback does not produce any blue smoke whatsoever, and I ran Ravenol DXG with a NOACK of 6% and it still used about 0.75 quart over 3k miles. Excessive? Not by any normal measures, but enough that I would have to add oil on a 7500 mile OCI as recommended by the manufacturer. I've got a mix in it now of PP Euro 0W40 and PPHM 5W30 which seems to be doing better, but the Subarus I've had all seem to experience a high jump in consumption when they are driven for long periods at speeds of 70+ which is typically 2800+ RPM. OP, have you been able to discern any changes due to driving conditions, or is it always the same regardless of driving style and speeds?
I think at those sustained engine speeds and the design of the boxer motor simply makes more oil mist from the thrashing going on, and it gets sucked through the PCV, but around town and 55-60 there is very little to no consumption. I'm not sure if thicker is the answer but hopefully some testing will reveal which oils are consumed less, which can then be used to analyze the specs and see if something jumps out.