Ian the second set is where you are suppose to put the arm if you want it level, as far as I know all lights are designed that way. The first set will make it tilt down slightly.
It could be that the arm is slightly higher than level. You just don't notice it until the fixture is installed..... I'm guilty of putting my M-400 all the way up when i install it. The slipfitter rocker idea was pretty poorly designed. The light mounts like a floodlight if you push it in all the way....
I liek ti too, but it is poorly designed. Leveling my M-400 when i'm putting it on the arm is a pain the the @$$. The thing weighs about 45 pounds. imagine the M-1000. I think those kept the origional 60's slipfitter though. Not sure. It seems the M-1000 (aside from the changed door) remained the least changed light in the M-series.
The Cooper ignitors (the real ones ) are actually based on an old Westy design and have spade terminals. The square Caster ignitors have wire leads and are made by Caster.
And Niall, what slipfitter does the R7 use?