25 and 50 yards hold.

I find six o'clock hold to be the most effective for me at 25 yards. When I try centerhold , I have a problem aligning my sights in the center of the bull.
At 50 yards , I dont have that problem . Does this make any sense?

target closer so you are looking at it i guess.

Fundamental:  Align the front and rear sights.  Hold on an area of the target.  "Aiming" is over rated, sight alignment and maintaining sight alignment within the area of hold is critical. 

However, the issue may be that with a center hold there is less perceived contrast between the sights and the target black. The closer the target is, the darker the black can look for some people.  Essentially, the "bars of white" between the front sight and the sides of the rear sight will tend to become "grey" for those people. There is simply not enough contrast to help with the perfect alignment of the front and rear sights.   Hence you will find that people tend to group into "center hold" and " 6 or sub 6, etc hold".

Use whatever makes the front sight and the "bars of white" look the best for you.  Again being able to see the exact relationship of the front and rear sights is way more important than where we hold on the target.