As one who has been progressively circumcised, it isn't just about wyere the scar line is and wherher frenulum is, but also how much skin is left.
A fair numebr of guys may have bare glans in underwear, but are fairly loose when hard , loose enough to move skin up"down with some covering glans on the upstroke.
A couple of examples:
These screen grabs from various videos I collected over the years when I was semi cut. Interestingly, these models have bare heads as they undress, but mine was partly covered when soft, yet once hard, I was like the above.
Visually, you have not much clue that the skin can still move up enough. Looks fully cut, smooth skin on shaft with no wrinkles. And where you grab shaft makes a huge difference.
The first time I compared with a cut guy, I got a big surprise. I had told him my skin could still go over head on upstroke, yet, because of the way he grabbed it, the skin stopped at the rim on the upstroke, just like on his dick. This had never happened to me. I then grabbed mine and showed hom how the skin could still go up. In hindsight, I think you have to grab it lower so the stroke is longer and you can push skin over the head.
On a standard cut , you tend to grab shaft higher up since skin moves less such that on upstroke, either your fingers or the skin gets to touch the rim of head.
And on a tight cut, you don't bother trying to move skin and rub it instead.
Obviously, for foreplay when you just touch the penis to "tickle" it, then all the areas such as inner skin, circumcision line and frenulum area become really important. One study at Queens University doens afew years ago found the circumcision line to be the most sensitive for RIC guys. (I still find my glans sensitive but I am not RIC, but I have been cut long enough that I am not siure if different from RIC now).
For uncuts, there are variations. When I was uncut, I made a point of fully retracting skin on downstroke. But for some guys, they don't want foreksin to uncover coronna and come back up over it, so foreskin needs to remain over part of head on downstroke. Otherwise, it is pretty much all up/down of foreskin.
But for cut guys, the variations are huge in best technique to pleasure him. When enough skin left, up/down of skin.
For me, prior to my current circ, I would grab shaft with fingers near rim of glans and the slight up motion allowed by skin would gert fingers to rub the coronna.
Now, my skin has no movement and I have coverted to 100% rubbing and for the last couple months, with coconut oil from start.