rich p said:
Ah! all is revealed my Dear Watson.
In that case yes the longer cage is the route to take .You might fiddle a short cage to work but its always going to be on the limit of adjustment as the others have said.
The problem is the amount of chain you are going to have to accommodate the big ring and big sprocket combination, (although you would be unlikely to use such an extreme alignment.)
When switched to the small chainring and smallest sprocket there is too much chain for the rear mech cage to hold hence the jockey bouncing on the sprockets.
