What you would expect to find:
1) If the earth is flat, you would see that the moon never disappears by the set time.
2) If the earth is round, you will loose visual on the moon by the set time.
I don't think that's accurate, as we've just spent a lot of time discussing multiple reasons why something could disappear "over the horizon" at the set time, including distance, atmospheric conditions, etc. What was "set time" determined by and who determined it, i.e. what "authority" determined that time.
I just don't think you'd even get consensus on when conditions were right ot take the proper readings.
If you look at the history of even the 6-mile Rowbotham experiment, they went out there multiple times on a wager, and each time they were thwarted by fog, other effects on visibility, etc. So the one time the glober claimed to have won (there was a monetary wager) because the flag on the boat disappeared, but then there was fog that night, and it went to court and the guy got his money back.
While not "stupid", I think that you'd have to have every potential objection addressed.
So, for instance, we have plenty of stuff out there where things can be seen too far, my favorite being the one lighthouse that reaches only 200 feet above sea level, but was photographed from about 237 miles or so (from memory) away by some professional photographer whose picture was then certified by some agency. So, the reason this is compelling is because it was NOT done by a Flat Earther, AND it was certified by some agency ... so you can't claim it was just faked by an FE with an agenda. Photographer taking it didn't even think to consider the curvature problem.
So you put that out there, and the globers refuse to accept because they say the magic word ... "refraction". Yeah, sure. From 150 miles away, where the degree of refraction would have to be perfectly the same from one yard to the next for 200 miles, otherwise, if you had slightly different rates of refraction at any given stretch along the way, the light from the image would clobber light that came in with different refraction rates, resulting in at best an incredibly blurry image, if it were visible at all ... and this thing was crystal clear, meaning the rate of refraction remained absolutely constant for 200 miles. Ridiculous. But, the point is ... if you do your experiment, depending on which side it favors, there will be some explanation for it, whether legitimate or not, whether it's just saying "refraction" or they say that there was excessive humidity in the air causing the moon to disappear prematurely (let's say if it sets before either model would have it setting under ideal conditions).
Just too much variability, and too many people would dispute it.
I think they do have technology out there, especially the DoD that could effectively do laser-leveling using a combination of GPS and other techniques where refraction cannot happen ... but they likely won't release that. There was the one group in Brazil that constructed an ingenious experiment where they took two skyscrapers that were miles apart and had some sophisticated GPS tech accurate to within a couple centimeters. If the earth were a ball, the tops of the skyscrapers would be farther away from one another than the bottoms, since the buildings would be built perpendiculate to the plane beneath it and would therfore lean away from one another on a ball, whereas on a flat earth, they would roughly be the same distance apart. They said that their equipment reigistered that the respective tops and bottoms of the buildings were exactly the same distance apart plus-or-minus the accuracy of the equipment (which was very high and could not account for explaining away the result). Unfortunately, I have no been able to find any publication with the results, and of course anyone could claim they just made up the results, so we'd have to replicate the experiment. But the point is that I do believe that there's some apparatus, some scientific equipment, out there that can settle the claim. Not sure about this advanced GPS these guys were using (they say they had to borrow it from a university where they had one of about a half dozen in the entire country) ... but I'm sure the military has stuff too.