It's gone in stages: can make 10 pins, cannot make them some nights. Can make 6 pins sometimes, sometimes cannot. This has nothing to do with throwing a ball straight. I can throw any ball on any condition nearly dead straight with aim. It sounds easy but if it was then everyone wouldn't be using a hard ball for spares. Before I had found a old beat up Nitro urethane at a Goodwill of all places. Got new grips for it but the thumb was horrible. Tried to get it fixed but the pro shop messed it up more then tossed it.
I recently got my Mom a Maxium which had one of those long ago. I'm thinking about the same thing. Not just for right side spares but for 4's and 7's. When throwing the urethane as long as I didn't hit up on it too hard I could get behind the ball and still throw it straight which is a problem obviously with strong resin balls. It's become obvious to me getting behind it to a light extent like on my strike ball I have better control of aim then breaking my wrist throwing it straight. I guess to each his own. I have a 3 bag roller and on most nights will use 1 of those balls only and other times 1 more in practice or a 2nd or 3rd game so it wouldn't be a big deal to use a "ball space" for another ball I usually only test in practices.