Here are plans. Its as simple as i could come up with, with just one angled cut, its not tested with fancy gizmos, just with my ears, and i am a mere amateur when it comes to design and building. I seem to have got the bug after finding this site! But i'd like to see what people think. I consider this a great little wedge for a tidy price.
Measurements in millimeters, any questions i am available on rossATbluebirdsoundDOTcoDOTuk.