Fasttrak

Having just completed that section last night I think I can answer this one. The strap is mounted at the rear to the waterfall and is a fixed mount, no up or down adjustment available. The front goes into two fixed plastic pins that have no adjustment. To use a shorter lipo you are going to need to implement some foam on top of the battery to keep it in place. TLR could release a new waterfall and forward pins but I doubt they would bother. Not sure if the sliding lockers would engage a shorter battery to keep movement of the battery in the tray, gonna have to try with your short lipo and report back.