After diving a specific way for many years (20+), I was introduced to the GUE / DIR way of diving. There were a lot of things that were different. I never had to clip my primary reg whenever it was not being used, I never had to unclip my SPG to read it and have to reclip it back. Just some examples of things I had to practice.
Having to deploy a SMB (Halcyon 6') from my backplate pocket was another strange skill that took practice. Most of us carry our smb's in that pocket. We all dive with Drysuits. We all practice deploying the SMB's /liftbags early in the season to get that muscle memory thing reviewed well. Some of my buddies carry their smb's in their left pocket ( DUI Large Bellows zippered pocket).
When I took the DIR-F class, I was a basket case with most of the skills. After commiting to the whole DIR concept of diving, I realized I had to practice the skills to keep sharp. It took me a year to get good enough to kick backward with my drysuit. I could nail that skill with a wetsuit (3mm) on every time, but in a drysuit it was different.
Wherever you decide to put your SMB/liftbag. You will need to practice deploying it from that location. If you use the backplate pocket is to be used to stow the smb, make sure you set it up correctly. When you clip the smb to the butt d ring you have to make sure it will deploy without wrapping around your crotch strap. This happened to me when I decided to pull the SMB with my right hand instead of my left.
Good luck,
Jim