Are post offices in competition with each other?

I live roughly equidistant from three post offices. Two of them are fairly small – the old small town post office where everyone knows everyone and it’s pretty laid back.

The other one is a big branch PO -probably 100 parking spaces, easily 75 delivery trucks work out of there – it’s the main post office for one of the more significant suburbs here.

When I have to mail a package, I sort of randomly choose which one to go to. Today I had to drop something off at a store near the big branch PO so I went to that PO to do my shipping.

But am I in some way hurting the little ones (L1 and L2) by going to the big one (B1)? Do post offices get ranked by how much income they bring in? Should I go to L1 and L2 more often in order to keep them as active facilities?