the correct way to add the right thrust is during the building process.usually 2-3 degrees is all that is needed so the direwall is built with that amount of offset in it.then the engine needs to be mounted off ceenter a tad to put the prop back on the centerline.trigonometry helps give you the required demension when you decide on the amount of degrees.I split the difference and use 2.5 degrees.And yes it does help on scale aircraft with conventional gear.but as others have said,if the plane is already built then adding washers or wedge shaped shims behind the mount will work fine.I prefer to have the entire engine mount secured to a solid back to prevent any distorting or unneccasary stres that could cause flexing or a crack and use thrust plates or even cedar shingles that are fuel proofed and mounted behind the mount,gives a solid ,strong backing to the mount.