Thanks guys, that answers several questions.
It probably says, if you don't need the extra height to shoot comfortably, don't... because the added height would require more shimming at the back. Correct?
Last question that remains would be, how come I'm not particularly uncomfortable with my One Hundred, even though my scope sits just above the barrel?
That's probably because I've adjusted the butt hook down so that I pull the entire rifle up a bit...
The Filthy Pig
: Air Arms 100 (1990) + AA Olympic trigger + Welham reg + Custom Shop CS1000 stock. Status: leaking.
The Unknown Quantity
: AA EV2 Mk4. + BSA Platinum 10-50x60 + Jon Harris wheel. Status: sorted up to 25 yds.
The Limping Dog
: Air Arms Shamal (1989) + unknown origin sporter stock + Optisan Cobra 3-9x42. Status: slowly leaking; needs work.
: HW97k + Venom Lazaglide. Status: working just fine; needs scope.
with apologies to NJR100