Which one to pick (extended vs. SPR) will depend on your scope and where you want the eyepiece to end up. I went with the SPR mount which puts my P4Xi further forward than the extended. You have to play around with your scope and figure out where it needs to be. Look at where the turrets end up relative to the receiver, then pick the scope mount that places the rings in the right place on the tube. A good point to start would be with the eyepiece at the end of the upper receiver. Move it forward or backward depending on how you shoot and the eye relief of the scope.
https://aeroprecisionusa.com/scope-mounts.html

