Hi,
You're right about the springback, so I'd add that if I measure 1.4710" headspace, it will definitely be 1.4715" or even 1.4720".
At this point, setting a 1.4690" headspace on the die should give me excellent bolt closure, but that's not the case.
So the hypothesis that you support, that it could also depend on the body taper, is plausible...
It seems strange to me, however, that there is a difference in dimensions and proportions between an FL die and an FL Bushing die from the same manufacturer, especially from a specialized company like Forster.
I haven't tested the repeatability of the measurements yet because I'm still trying to find the right die setting and I don't have many fired cases to resize.
Okay, regarding the case life reasons.
To measure headspace, I use the Hornady .375 comparator, which doesn't seem to be CIP-compliant.
The SAAMI or CIP measurements are like a love manual; they're useful as long as you can read them. Once the light goes out, everyone makes do as best they can...

I put a drop of silicone oil on the bolt lugs.