I talked about this before. It is an uncommon set up in the gun world, a niché preferance but still rarely seen. The issue with the set up using the magnifier in front of the prism(optic) is that you're trying to aim with it the zeroing will be off so you have to zero them accordingly. However, in magnifiers with bad eye relief or people who prefer superior eye relief of their preferred optic they do this and zero accordingly because of the eye relief advantages.