and for a tall building on the bay, refraction would complicate any sextant reading to the point of doubt. In my view, only a rigorously performed weather balloon experiment would settle this. No mining survey takes account of earth curvature, nor any civil projects such as the Delaware, Paijanne or Dahuofang aqueducts.
You're asking questions that demonstrate to me your critical thinking. I suspect you have some real talent.
There's a lot to say for fully answer the "tall building" experiment. You really need to combine a second type of observation, disappearing hulls first of ship going to sea, or maybe the sunset time by floor if the building has windows looking westward to the horizon over the bay. (Otherwise, FEers invoke special pleading about the "magic" nature of sunlight's limited travel distance through an atmosphere ("atmolayer").
Regarding refraction, I agree that it makes for variances in the experimental results--but just in a numerical sense. Refraction favors longer distances, and longer distances favors RET. So refraction limits your experiment's repeatability , but not that the predicted difference between the two theories exists.
Next, and I love this question: can we quickly dismiss FET with a personal experiment with a helium balloon and a camera? Yes, and in deed, it's easy and inexpensive. First, the standard middle-school-level experiment that you'll see on youtube regularly shows a curvature. RET predicts this curvature. FET tries to hold on with some special pleading: That's just the curvature of the Sun's illumination on the Earth's surface. Tom Bishop even once argues that you could squint your eyes to make out distance countries in some examples. So, you'd need to add another constraint to break the special pleading. (Of course, the Sun illumination is not a circular except on the first days of summer and winter. On the equinoxes it's a straight line.)
Launch the balloon an hour before sunrise or after sunset. The launchpad will be in darkness. The balloon will rise into the sunlight and be able to see the terminus. The terminus will be curved. RET predicts that. FET can't handle it. Example:
So for about $1000 any FEer can prove FET false without any concern about the Conspiracy's interference. Or they could just vet the video I linked as an example and give up now.