There's no hard-and-fast rule about whether the problem is best fixed with a different temperature plug or a different compression ratio. You basically just have to play with it until you get it to run well in your climate, your running conditions, and your fuel.

Pinging hard while decelerating sounds like the LSN is too lean, but if you can't enrich the LSN without the engine slowly loading-up on fuel and choking-out when accelerating again after idling for a minute or so, then the pinging during deceleration might indeed be the plug is too hot.

The general rule I use for selecting a compression ratio is to look at the range of "acceptable" tunes that I can achieve. If I have to tune the engine so rich that it loads-up on fuel just to keep it from overheating, then the compression ratio is too high and I should add a shim. If I have to tune the engine so lean that it makes bad "lean engine" noises just to make sure it warms-up properly when running, then the compression ratio is too low and I should remove a shim.