If the alum. ring is sandwiched btwn. phenolic then how is it that the wood is shrinking. The wood has nothing to do with it nor does the phenolic. Neither one is shrinking. It's 'pinch-down' of the finish.
As the applied finish ages, it continues to cure. As part of the curing process, it contracts or 'pinches-down' on whatever it's applied to. This phenomena is very real. Ask any auto-body painter.
What complicates this is that the metal rings don't sand down as readily as the mtrls. adjacent to them, be it wood, phenolic or whatever so even though you think that the rings are sanded flush with everything else on the cue, they really aren't. Aluminum rings are the lesser offender here because they do sand down more easily than nickel silver, stainless steel, and etc.
As long as buyers insist on having metal deco rings in cues, this problem will persist. About the only remedy that comes to mind is to coat the cue with a substrate sealer that is so hard that it doesn't allow the clear top coat to pinch-down any further than the top surface of the substrate itself.
Dick Neighbors applies a UV cure substrate under his clear-coat and I'd be anxious to ask him if this cured this problem for him and is he able to detect pinch-down on the rings after the cue has aged somewhat.
Another substrate coating that Prather informed me of many years ago was to entirely seal the cue with CA before applying the clear-coat. This could have several benefits; sealing oily/resinous wood, filling pores in porous wood thereby reducing the number of times the cue will see the spray booth and possibly preventing the pinch-down effect on metal rings. The one remaining question I have is how well does it allow for full transparency or D.O.I. (distinction of image). I guess I'll just have to try it and find out.
FWIW, I have many cues out in the area that I built many years ago using alum. deco-rings and to this day, you still can't feel the rings. No substrate was used, just clear-coat.