Roland and Yamaha have two completely different ways of reading expression from a continuous potentiometer (found in expression pedals). You cannot use a Yamaha with a Roland, and vice versa. It's not the polarity, but the taper (or slope) of the pot. Something about linear vs. log., or something like that.

Basically, if you want a pedal for Yamaha, use a Yamaha, or a Behringer (they are Yamaha compatible, and very good for the price). Roland... use a Roland (I don't know of a good inexpensive alternative to Roland)...

As you have noticed, although it SEEMS like they will work, you get ALL the action in a tiny fraction of the pedal's throw. Not really usable, IMO