You are, unfortunately, right on the money. There is horror, and it is due to the FOV magic/weirdness.
TL;DR if you're using MDV 0%, the horror is that at lower FOVs/higher zooms, the parts of the screen that are far away from the center will become slower and slower.
At low FOVs/zooms (in other words, hipfire), the center of your screen moves very slowly and the edges of your screen move very fast. At high FOVs/zooms, all parts of your screen move roughly the same speed. Therefore, you can only ever match the speed of your screen at some set distance from the center:
The recommended choice is to match the speed of your aiming reticle at every zoom level (otherwise known as MDV 0%), because if you can only train muscle memory for one part of your screen, the reticle seems like the obvious choice. However, because the center of your screen is the slowest part, as a consequence the speed of the edges of your screen are drastically mismatched. As you zoom in more, your sensitivity for the majority of your screen will slow down.
The other common choice is to match the speed of a circle of pixels whose radius is 75% of the horizontal distance from your reticle to the edge of the screen:
This is how counterstrike and battlefield do it by default. The circle is a nice distance from both the edges and the center. It basically tries to minimize the mismatch, so neither your screen edges nor your reticle are that mismatched. As a consequence, your sensitivity feels roughly the same at all zoom levels.
However, this is not recommended - it feels good, but in reality, only the pixels that lie along the red circle have a 1:1 ratio at every sensitivity, so that part of the screen is the only part you can truly build muscle memory for. This is arguably useless - how often do you need these exact pixels to move the correct distance?
The reality of the situation is that you have to train your aim on every FOV/zoom individually to truly gain the muscle memory - you can't train on just one FOV. However, you can cheat a ring of pixels of your choosing, and gain muscle memory for that ring of pixels for all FOVs. Arguably the most important pixels are the center, which is why I recommend MDV 0%.
Also, for some reason, Apex's rifle/lmg/sniper zoom sensitivity setting is the same as the smg/shotgun/pistol ironsights sensitivity setting, despite the two having different FOVs: This means that if you choose to not use MDV 0%, then either your rifle/lmg/sniper ironsights or your smg/shotgun/pistol ironsights sensitivity will be incorrect.