Knife-edge effect in 2 m and 70 cm

Studying the 2-m and 70-cm repeaters I can excite every day from home (IM98ri99) [that is, without the help of tropospheric ducting] I have found that about half of them are behind rather tall mountains; I suspect the knife-edge effect or diffraction on the crests of these mountains is the reason. In the picture, a 1050-m peak (Penya del Salt de la Mort, EA5/AT-056, IM98mi36) at ~40 km from my place is possibly the reason why I can reach a REMER repeater at Ardal (EA5/AB-032, 160 km, IM88ti76) from home every day. Here is a heywhatsthat.com profile for it.

 

Here's another example:

I reach the (wonderful) 2-m and 70-cm repeaters at the summit of Cocoll, 1048 m [ED5YAM, IM98wr26], 52 km from me, not despite the ~1400-m ridge 38 km from me [IM98vp15, part of the Aitana range], but probably because of it. 

So, perhaps, 2-m and 70-cm ham radio is not only about line-of-sight, tropospheric ducting, or satellites. You can be surrounded by mountains and still reach far with their help.

[Edit: September 29, 2024]

Yesterday, September 28, 2024, a number of people climbed up to SOTA (summits-on-the-air) summits to make VHF FM contacts. According to the forecasts, we could not expect much help from the troposphere. There was one 235-km QSO that I liked a lot, between EC7ZT Manu, who was on top of Ruero, EA7/GR-043, and me at Serra del Flare, EA5/AT-059. Solid copy both ways, any time during the activation. Here's the profile (I'm on the left). The curved line is the line of sight.

Was that obstacle about ¾ of the way, not far from Cerro Poyo EA7/AL-005, helping us? I was using a hand-carried 4-element log-periodic antenna and about 4 W, and he was using about 5 W with a telescopic vertical).

This is not the only amazing QSO. There's also this other one with EA7KJH and EA7KUG who were at Veleta EA7/GR-002. It was harder.

I wonder how this last worked!