I've got Andy Lennon's book in front of me 'The Basics of Model Aircraft Design' and he suggests that spoilers are hinged at 20% chord with the spoiler being 10% chord. He suggests about 50% span.
All the RAF fighters I've worked on or have seen have for want of a better word 'barn door' type spoilers. In particular the Tornado.
I wonder how much the wing loading affects the type of spoiler you use. and would a higher loading reduce the amount of proverse yaw.
Dave