Getting a red dot sighted in. Got a "hello" on my middle finger from the trigger guard! IYKYK
Frosty, part of the issue may also remain in the grib design of your 88b. Compare it with your 500, curious if the 470 may feel like the grip is a bit more closed, like turns downward more abruptly vs. a more swept-back, open grip.
The stock and especially grip area of the 89b differed from the 88b in this regard. Chris Sells said Heym ultimately transitioned towards a more uniform grip and buttstock design using that of the 89b...but couldn't tell me what year it started or when they were supposedly the same thereafter. What I know is my 470 88b used to knock the hell out of my second finger, and I had JJ set the proper LOP for me...it was simply a function of my XXL hands and smaller, closed grip design. My second finger still actually has scarring on it from that rifle. The 500NE that I received in the trade with Franz, your 500, did not contact my second finger all that much at all...but still did it on occasion.
That 500 of yours was in the frame design changes for the 88b, when they still had the bolstered frame sides, but had radiused the bottom frame corners, making it much more comfortable to hold or have on a shoulder if so inclined. I don't have a photo of your 470 88b, but seemed to recall it was a year or two newer production, with the updated frame that deleted the bolsters on the frame sides....but likely before any stock changes.
Heym came out with the 89b in 2016, but am thinking the first rifles may not have landed in the US until early 2017. (my 450/400 was in the first batch of 89b's which is why it was delivered with a fancy saddle leather take-town scabbard serialized to the gun) It would at least make sense that any stock design changes to the 88b would occur either as they are making the 89b or sometime soon after getting the positive feedback from the customers. The open grip design is something that larger-handed folks really appreciated, so makes sense they would have built the change into the 88b as well....its the when that I still don't know.
Each time I've acquired another Heym, I try to look at them together, take some measurements, and just enjoy learning some of the similarities and differences. This is one I have not nailed down yet.