It seems obvious to me, from flying, that one runs out of signal strength long before it gets blanked by the earth's curvature.
Not my experience. It often seems possible to pick up an ATIS close to the VHF horizon. Other factors, including terrain as you cite, play a part in reducing the practical range on many occasions, but it's worth knowing roughly how far away the horizon is, as much to know when it's
not worth trying as when it is.