I have both Alpine and Trail Loops and mine fit almost exactly as in
@Boardiesboi's pictures. My wrist appears to be just slightly larger, as the Alpine Loop fastens one stop down from theirs and the Trail Loop closes right at the center underside of my wrist. That's with a medium Alpine and a S/M Trail.
If the medium Alpine Loop fit you similarly, I think you should consider the M/L Trail. The Trail is an odd duck because it comes in S/M and M/L just like the Sport Loop, and is indicated to fit the same size wrists in mm, but the Trail Loop is shorter than the Sport Loop. This makes it a bit of a squeeze to get my hand through the loop and also causes the fastener to fall in the most undesirable location, right at the underside of the wrist. The S/M Sport Loops, which again are for wrists with the same measurements, do not have either problem because they are about an inch longer.
I ordered my watch the Trail Loop and on experiencing the tight fit of the S/M, attempted to exchange the band. I had planned to get an Alpine Loop anyway so was going to swap for that one since Trails are not yet in stores. Unfortunately, I learned from the retail staff that Apple has not given them a way to swap bands on the Ultra specifically -- they can do it for the other watches -- so I would have had to return the entire Ultra to swap the band it came with. Wasn't going to do that, so I'm using the S/M but wishing it were a M/L.
Anyway, choose wisely!