Shimming on the Alpa is indeed to get the sensor plane in the right place with respect to your lens at infinity. If you need to adjust for off axis correction then you can achieve this by cutting down a shim and placing it in the appropriate place, although this is atypical.
One slight consideration with the shimming is that you normally do this with your longest lens since this makes it easier to view distant objects. However, the resulting adjustment between the back and the lens is really only correct for that lens on the body. The assumption is that all lenses are adjusted to perfection and I can state from personal experience with my Alpa Schneider & Rodenstock lenses that sometimes this is NOT the case. For example, I just had to have my 47 XL APO-Digitar corrected as it was significantly back focusing at infinity compared to my 90 Rodenstock HR-W & 150 Schneider. Now the adjustment for the infinity setting on the wide angle lens is very very slight and my dealer corrected this using their collimeter.
In all fairness it's probably also worth pointing out that precise setting of back to lens adjustment / correction can also be achieved with Arca's solution. That does have the ability to configure unique offsets for the back/lens combination on the body which in reality the Alpa shimming solution can only achieve for one lens/back adapter/back (with the assumption that this is the same for all other lenses you have of course).
Btw, I'm a huge fan of my STC. I traded my Max and gave up the dual axis adjustments for this camera but for travel & landscape work it's a superb lightweight solution. Compared to the space required for the Max, the STC is tiny and much more convenient. When you start adding longer lenses and the short barrel adapter to the STC (or TC for that matter), the camera pretty rapidly gains weight and bulk. With my 150 & SB adapter & P40+ on the STC you are looking at a camera that is as big and almost as bulky as the 645DF with 150D on it. However, with the 47mm it's very compact.
One last thing, I notice that almost without exception the Alpa and other tech cameras are pictured without the sync cabes for the digital back. The reality is that when you're shooting in the field there's always at least a sync cable from the lens to the back and unless you're using the finger shutter release there's also a cable release. For Phase One backs you may also have even more cables if you're using a wake up release.
Just trying to keep everyone honest here ...