You are not compressing the bedding material once it's hardened, you might bend the stock, bottom metal or action but you are definitely not compressing the bedding with action screws.Seems like there are a lot of variables to this and I would be curious to see the actual test. And for me I would assume that even at 5% shrinkage me just torquing my action screw to the correct torque would compress the bedding material, my pillars and the stock enough to remove the small amount of shrinkage from the issue. If I havent shot a rifle in a year, I would generally retorque it prior to shooting it any ways.
But yes as shrinkage is volumetric it ,might not show much . Like i said Speedy's test points to longterm bedding stability, but its not an indicator of the material shrinkage as that mostly happend prior to cubes being cut to size.