Need help with fixed iron sights

My Milspec groups 7" low at 25 yards.  My rear sight is .25" high, front sight is .22" high, distance between sights is 6.37".  What height rear sight do I need to get into the 10 ring?  It gives me a headache to think about it.  I know I could lower the front sight but I think I would rather replace the rear.
Thanks
Phil

https://www.dillonprecision.com/sight-correction-calculator.html

Per the referenced website the correction is approximately 0.050 removed from the front or added to the rear.  I think the rules state “As Issued” so be careful with what sight you insta. It should be very similar to what is currently installed. 

I would recommend shooting the gun some to ensure things wear in a little. My MilSpec actually lowered point of impact after shooting it some. Next try a heavier bullet to see if POI will raise. Finally determine the load you want to shoot and file the front sight down. 

Midway has a Colt rear sight that is 0.320 which will raise point of impact 10 inches. Then switch to lighter bullets and lighter load to lower POI

Replace rear sight with an adjustable one?

thanks.  The formula was what I was looking for.
Phil