Hello,
It is not the fact that the rails are narrower that gives a problem (this is normally a standard dimension) but the distance between the nose of the saddle and the rails. Too short, the nose will then interfere with the plastic saddle mount.
Blackstridaaustria provided the explanation here
But you are right, the C17 being based on the B17 which does not fit the Strida, we can conclude it does not fit either.