I would recommend the 1.00" rings instead for that setup, particularly if you want to run flip-up scope caps as well.
The Vortex Crossfire II Hog Hunter 3-12x56mm Rifle Scope has a 30mm diameter tube. So these Seekins Precision 34mm Tube Rifle Scope Rings will not fit your scope. The 30mm diameter rings at the link below will work for that scope, but the correct ring height you will need will depend on the scope base and rifle you are mounting it to. The second link below will take you to a guide that will help you determine what ring height you will need.
https://www.opticsplanet.com/vortex-pro-series-30mm-riflescope-rings.html?_iv_tube-diameter=30-mm
https://www.opticsplanet.com/howto/how-to-how-to-measure-scope-height-scope-ring-height.html
To mount the Athlon Ares ETR 4.5-30 x 56 rifle scope to a Christensen Arms MPR I recommend using the 1.26" high Seekins Precision 34mm Tube Rifle Scope Rings.
Yes, these should be compatible.
You will be best suited with the 1.26 height rings.
You will want the 1.46" rings.
That scope would be tube size of 34mm and also for ring height High since its the Burris XTR II 8-40x50mm.
You will want the 1.26" high rings.
You would need the 1.26" high rings.
You would need the 1.26" high rings.