So let's get this straight you would take a 15 year pay cap at RPI +0.5% and you would be happy with that because all of it would be pensionable. You won't however accept a 15 year pensionable pay cap that allows you salary to rise by more but your pensionable bit to remain capped at RPI + 0.5%. Are you sure about that?? or is it that you just want a guaranteed pay rise for the next 15 years??
I'm not sure that was what FlyBhoy's post alluded to, but I'll let him make his own reply.