Yes, partial circumcisiuon is possible, even on a baby. It all depends on how much skin is pulled through the device, gomco, plastibel or mogen. Generally, after the deed, the doc leaves skin behind glans, but after it heals, it starts to cover again if there is enough.
In fact, for many babies, they get partial coverage and after a couple years, glans has permanently grown out of remaining skin (and/or fat bad at based of penis diminsihed, causing same).
After I did mine, I left skin retracted so the scar would heal properly, and it stayed retracted. A few weeks later, I tried to "wear" my foreskin again, but it would slip back immediately, feared I had become circumcised. But tucking it in underwear by holding skin over glans did the trick and over the years the skin retracted less and less in underwear. (I suspect foreskin restoration principles with underwear keeping skin from retracting).
Similarly, if your skin is loose enough to masturbate by moving it up/down with it going over part of head on upstroke, it is likely that it will stretch over time so you retain your partial coverage.
Looking at what restoring men go through, I went through some of this after my snip in order to not become permanently retracted.