The BMW sport grips are shorter than the stock Yamaha grips. Most people won't notice an issue with this. If looks are all important to you, you will notice a gap. Of course, if you fill the gap with a throttle lock like the Vista Cruise or NEP, it's a useful gap.
The fact that you're concerned about the length of the grips at all raises questions.
The ribs and palm swell of the BMW grips make them much more comfortable than the stock skinny flat grips, for many people. Some prefer larger grips still, and opt for foam or Grip Puppies.
The BMW sport grips currently installed, (my second set in 115k or so), measure 130 mm with the throttle side slightly shorter.
FYI - The FJR might use 135 mm grips, but it doesn't
"need" them. It's far more likely that Yamaha just had lots of them left over from the sport bikes. The grips were one of the first things to come off of every Yamaha I've owned. Stockers suck!