Pictures always help.
So you can see there on the right the mag catch from one of my 1911's, and the shelf on the catch identified by the arrow on the right is what actually captures the magazine by locking into the notch on the magazine on the left. So where that notch and the shelf line up determines where the magazine is going to sit in the magwell. The following picture shows the magazine inserted into the frame with the magazine catch removed, and you can see then the notch in the mag and where it would then lock up with the catch if it was inserted.
So if a catch for example got excessively worn then you'd see the magazine sitting ever so slightly lower in the well, or if the notch in the magazine was cut higher on the magazine body it would lock lower as well. The EGW magazine catch
I'd mentioned actually has that shelf on the catch machined about .020" higher than a standard catch, which means if look look at the second picture that the magazine would have to be inserted .020" higher into the well before it locked in place. Hopefully that clarifies it a little.