I normally use a solid lifter and pushrod with zero lash to check the rocker arm ratio with either the spring that will be used on the motor after getting the cam degreed in and or a soft checking spring for dialing in the cam timing and checking piston to valve clearances. I've seen around .012 to .020 lift loss at the retainers from the soft spring to big pressure roller cam springs
My next engine build will be checked with both 3/8x.125 wall thickness Manton pushrods and 7/16x.145 wall thickness to see exactly how much lift differences there are between the two at the retainers The search for knowledge on racing parts is never ending
BTW, you can use a drill motor and priming rod to check the actual lift at the retainers while priming the motor, caution it can get messy also