It doesnt matter how think the collar itself is, it matter where the ridge inside the collar is located as compared to where the OEM collar rests. It is that gap that matters, not the thickness of the collar itself. If you view the Camburg collar, the ridge inside is about 2/3 down, I am unsure where it is located on the the RPG.
I had Eibach 1" on my Raptor and it sat almost dead level on the passenger side and about 1/2" lower on the driver side. Can't beat that for being level, anything more and the truck squats, especially under acceleration or with a small load.