We can talk about the numbers if you want, in relation to the mountains you can see from where you live, but the problem is the surrounding area. If the elevation drops over the next 25 miles, you're going to be able to see much further as you effective are looking from a higher location to a lower one. The only real way to test that (as I mentioned before) is to look at something that doesn't have an elevation change.
Light can refract well over a mile, different temperatures and pressures do some funky things with the way it moves through different mediums, I mean, stars twinkling is a form of light refraction. Also, a mirage for example, can literally look like a reflection in the sand, because the temperature of the sand is causing the light to bend upwards. I found a picture:
Light bending a few hundred feet over many miles wouldn't be out of the question.
The elevation raises by a couple hundred feet.
I'm sure light can refract if you're looking up directly into all the moisture, pressure, and temp differences. On land these variables should be about the same.
I'm not opposed to a few hundred feet of refraction but we are talking about over 5000 feet.