if you would expand on the front aperture as to the size vs the target size..
The 'standard suggestion' is to use an aperture that appears about 2X the size of the aiming black.
Smaller than that and mental frustration can happen if the bull creeps into the aperture ring. The frustration increases the physical and mental process of 'settling down and getting a good sight picture'. When aiming, frustration MUST BE eliminated because it interferes with the primary goal.
The 2X ratio is good enough to SEE when the bull is centered.
Of course, everyone SEEs things slightly differently ....
so you need to find what works for you.
Endwell NY USA