The first thing I check is for the feet to be properly grounded because the sound post is carefully adjusted relative to the bridge foot. If the bridge gradually rocks forward the feet lift and its pressure point becomes further from the sound post. This will alter the sound and response as well as the height of the action. Because of the combined angle of the strings across the bridge the windings often split and dig into the wood, pulling it forward as you tune. For this reason I like to leave a little more thickness in the bridge top to spread the bend in the strings. One answer is to round off each side of the grooves with a tapered rat-tail file (needle file?) and to rub a soft lead pencil in the grooves. Another was the curved metal protectors that came with Pirastro strings and sat in the enlarged grooves. I don't know if these are still provided (Bel Canto lover !). Years ago ago we used to also bend the strings over small pieces of velum (drum skin) lubricated with lead pencil in the grooves.
