The altitude of Capel Curig is a little over 600 ft or 185 m and 2612 mm annually may seem very high for such a height but it illustrates that in a wet mountainous area the rainfall in the valleys can still be high. This effect can even be seen here on the North Downs, in a small way.
Bet nobody pronounces the name as the locals do. :-)

Tudor Hughes, Warlingham, Surrey.

The effect is very evident in Cornwall, where the hills enhance the rainfall progressively, with little dip between. In fact, due to the additional effect of convergence rainfall, the main factor overall is really distnce from the spine of Cornwall. If you had no knowledge of orographic rainfall, you'd struggle to pick it up from a rainfall map of the County.

To demonstrate:-
Headlands exposed to the west where there is no orographic enhancement on the prevailing wind get around 800-900mm (Scilly 865mm, Lizard 806, Bude 880mm)

But south coast bays, near to the spine are much wetter. Near sea level stations Penzance 1140mm, Falmouth 1102mm, Fowey 1173mm are as wet as Michaelstow on the western fringe of Bodmin Moor (1165mm)and wetter than than Culdrose on the Lizard plateau (away from the 'spine') which has 1032mm.

I've use generally 1961-90 norms, as I have figures for the greatest number of Cornish stations for this period. It's got a bit wetter since.

Graham
Penzance