My poor boy has NO side plate. I have seen washers inletted into the stocks, to help protect the wood from the lock bolt screw heads being screwed down to tight. ( Many T/Cs have this done). However, there is NO reason to crank those screws down so tightly that you are collapsing wood under the head, OR making the lockplate cock in towards the screw.
You want to seat the lockplate in its mortise so that the plate is at right angles to the barrel's side flats. If the lockplate is tipped in any direction, this will cause a gap to appear between the plate and the barrel. It also tends to bind up the internal lock parts, so they don't function properly.
Use a scratch awl to make a witness mark in the bottom of the lock plate bolts' screwslots, and a corresponding mark in the wood( Just a dot is all that is needed) alongside the screwslot where the bolthead comes to rest when tightened. That witness mark will allow you to return the bolt to the correct position over the life of the gun, every time you remove the bolts, and put them back, after cleaning and oiling your lock.