Hi... I'm not a Felt guy, but I've got some experience with gripshifters, and it was always my preference to run them with full-length grips, if the handlebar has enough room for it....and that seems to be the case with your current bars....(not sure what you're upgrading to)... but yeah, my hands always felt cramped on the shorter grips, and i didn't like to rest my hand on the shifter, b/c I didn't want to shift inadvertently while braking (my gripshifter experience was almost always on a mtb.... or post-repair/tune-up test rides back in my shop days...)
HTH