Hi Vincent
The active region on the Alpha is quite narrow, in the middle of the side. You do have to press firmly, but if you position your finger accurately then it's not excessive. Most people struggle with this to start with as they implicitly assume that the whole width is active, which it isn't, and that the sensitivity is the same all the way across, which it isn't either.
It's not inconceivable to replace the leather with something else (though this is quite a tricky operation, probably the most fiddly in the whole manufacturing of an Alpha in fact) but we never found a good alternative. The one thing that worked well was ultra thin PTFE, but sadly that's an exceptionally ugly semi translucent brown (and cannot be coloured) as well as near impossible to bond properly, so we gave up on that in the end.
Just writing this I'm wondering if there's a silicone based leather treatment that might make it more slippy. Perhaps someone should have a try - I know that silicones get used in leather treatment and there's no particular reason they should degrade the sensor underneath.
John