Over. Funny enough, I gave some serious thought to it to make my subconscious preference explicit and I believe this is about he direction of force application

Over. Funny enough, I gave some serious thought to it to make my subconscious preference explicit and I believe this is about he direction of force application to tear the sheet. See, with "over" it is straight down and cardboard roll on a (usually) thinner holder is already hanging on the axle under gravity and provides immediate resistance so the tear is immediate. With "under", application of force will move the roll forward and then - at best - there is some latency time before tearing force is fully applied. At worst, the roll starts spinning.