I wonder if the 105 is actually not wide enough.

Sounds strange but a 105 is like a short telephoto on a 6x6 camera, thinking of the vertical component of the 6x17 format a 105 is restrictive, I tried my 90mm on my 6x17 and didn't like it, but found the 75mm wonderful. Of course it depends what you are photographing, I could see a possible use for a 105mm or 90mm,(or even longer), in big wide open landscapes, the type that don't exist in the UK.

In general I use a 6x17 to shoot the shots not possible with any other 120 format, and also LF unless you shoot 4x10, 8x20 etc etc. So far I've usually found the 75mm ideal, just once or twice I've wanted wider