I'm going to give you my opinion on this as I have ran both the 12 and 13 inch revo-a's on my personal bike. This is a little long winded so please bear with me.
I put a set of 12" on my wife's 2018 Street glide special hoping to give her bike a better ride and lower the bike a little as she is a little "vertically challenged". I installed and adjusted the sag per the instructions with my wife for her weight and all her riding gear. After I got the setup done I took a test drive to see how they rode. I absolutely loved them! So much in fact I decided to get a set for my 2018 RGS. I couldn't believe how well they rode not even being adjusted for my weight!
I decided to order the 13 inch models for my bike, I'm 6'4" and figured with the extra length of 13 inch shocks would give me an even better ride. I ordered my 13's and after I installed them and adjusted the sag for my weight I decided to do a back to back test ride with the wife's bike and mine.
After riding them both back to back, I was not happy with my decision to go with the 13 inch shocks
The 13 inch shock is softer but it actually felt mushy or floaty to me. I felt like the bike handled sluggish to respond my inputs. Low speed turns felt like the balance was not nearly as good. It kinda felt like the rear end was too high and the front wanted to nose over in tight low speed maneuvers. I rode both bikes a few more times to really get a feel for it. Keep in mind I have ridden both of our bikes quite a bit so I am used to the difference in the handling of the different style fairings and both of them being 2018 Specials. So they have the same tires/wheels, etc. My last complaint was I just thought my bike looked tail high with the 13's.
I'm not saying that the 13's were terrible, just not as good as the 12's when ridden back to back IMO.
In conclusion after sending the 13 inch shocks back and having them rebuilt as 12's I'm completely satisfied. I really could not be more happy with them. I feel that my handling is better, it looks better, and rides great.
The suspension is soft enough that is soaks up the harsh bumps that I used to to brace for while eliminating all the little washboard bumps I used to feel. Small bumps or cracks in the road even tar snakes are all but forgotten. Best part is that I feel like the suspension tightens up and plants the tire in the curves while giving me a good ride. The responsiveness is back and the ride/comfort is better than ever!!!