If you use an impact driver first choose the correct size bit and tap it into the scew head on its own so it is good and tight in there. Then add the head of the impact driver and if it helps insert a socket extension between the head and the main body of the driver.Usually half inch drive. This gives good control in awkward places and allows you to get it lined up at perfect rightangles if you see what I mean. Load up the driver turning it the way you want to go and give t a solid thump with a club hammer. I have done lots of screws in this way it rarely fails.
Its all in the wrist action as they say so good luck.