Working in the historic sections of Minneapolis / St. Paul, I have seen my share of old masonry installations, and done new installs in masonry.
The worst problems in the old work come from conductors trimmed to the minimum length. . .
Second worst problem is created by the wood screw blocks set by the original mason having disintegrated leaving gaping holes. . .
I prefer to use small plastic anchors that are sized for the door button manufacturer supplied mounting screws. The screws tend to be #4, and sometimes as large as #6, so the anchor gets drilled in with a 3/16" (or smaller) carbide bit.
Many times, the aesthetic, that the door button has to match, will allow a choice of a wide or tall (or both) decorative button plate that will cover a multitude of goofs.
Door casing vs. masonry? The bottom line there, for me, is the placement that is most natural for the guest at the door. Part of what is sold in the installation is a "graciousness" to the client's guest-at-the-door.