Primary is running a sale so I want to pick up a mount for my new scope. The scope is a vortex crossfire II 1-4 and it's going on my ar with an ace stock and a 16" barrel. There are three options of mount all made by aero ones called the ultra light, next is the extended and last is the spr. They all look the same but it appears the difference is how far away the scope mounts. I think the ultra light is the one I need but I just want to be sure.