In order to cover the San Diego market, Tijuana TV and FM stations that have an interest in selling ads in San Diego County have to have good signals across the border.
When XETV 6 used to sign off at night, the announcer would say the transmitter is located on Mount Diablo, which I suppose is a high peak near the U.S. border. That way XETV could cover San Diego County as effectively as the U.S. stations. (My cousin who lives in Fallbrook says they get XETV 6 on their cable system, but oddly not XEWT 12, Tijuana's other VHF station.)
I always thought the four best FM signals among Tijuana FM stations were 104.5 XHLTN, 92.5 XHRM, 91.1 XETRA and 90.3 XHITZ. They are audible even in places like Oceanside and Carlsbad. And somewhere in the last few years, 105.7 XHPRS must have gotten an upgrade. Most of the other Tijuana FMs are so weak they have trouble beyond La Jolla.
Are they all on Mount Diablo? I suppose it's hard to get accurate info on Mexican FM stations' height and power. An old Broadcasting Yearbook I have shows XETRA-FM with 100 kw at 800 feet above average terrain. That's pretty good but I thought they'd even be stronger than that since 91X is audible in Orange County if you're near the coast. And a more recent listing shows them now at just 460 feet above average terrain.
XHLTN is even worse. I thought they had been running 100 kw on a 1200 foot tower. But a new listing shows them only at 57 kw at 350 feet. That can't be. I also see XHRM and XHITZ at 100 kw with 600 feet. But XHPRS must have found a very tall mountain because they're listed as 8 kw at 2500 feet. Why wouldn't all the big Tijuana FMs go to a 2500 high peak if they want to compete in the San Diego market?