As a training aid they do make a target card which has one diagram the same size as a normal diagram and 4 more which are 2 smaller than the normal and two larger than the normal,you put a group of shots on each and by looking at the group can decide which is best suited element size for you to shoot with,
That demonstration aid is alright for prone, but for standing the primary criterion is that all the shooter's movement during the aiming phase is contained within the foresight. An essential prerequisite is establishing a NPA centered on the target in order to accurately assess the degree of movement. The other problem when you employ a larger than normal aiming mark for standing is the tendency to focus on the target and not on the foresight.

If you want to demonstrate the effect of changing foresight aperture size on the resultant group it is best to do it with a variable foresight using the target you normally shoot at.

Rutty