1/16th is what I set my cowl and spinner at when I'm setting up A plane so I would say don't bother. If the cowl slides A little it isn't as bad as some people think, the back plate just rubs A little, no real harm done. If you must move the engine forward then use A sheet of 1/16th ply behind the mount to move everything forward, washers work but with the ply you will have even mounting pressure.