MMU2 and PVA: loading fails due to stringing during retract  

MMU2 and PVA: loading fails due to stringing during retract

Setup
Mk3 with MMU2
F1: Prusa Silver PLA (not Prusament)
F5: PrimaSelect PVA+ (purchased from Prusa store, in good condition and dried)
Firmware 1.0.1, all lengths calibrated (F1 with PLA, F5 with PVA)

Problem
The first time the PVA loads it extrudes fine. But when it retracts, it leaves a loooooooong string. In fact, a "thread" about 5cm long is left sticking out of the MMU2 body when the selector moves back to F1. Of course, this means when it attempts to load the PVA for the second layer, the string enters the selector, pushed by the rest of the filament. Then, the string (from what I can gather) triggers the FINDA early, causing the filament to never reach the Bondtechs and the PVA simply stops extruding. (In fact, I can see the thin string begin to pass between them, then the MMU2 stops feeding it further and the Bondtechs just continue trying to extrude air.) The PVA simply will not load the second time due to the massive string.

What I've Tried
Unfortunately the MMU2 settings in Slic3r do not have a PVA preset (only BVOH) so I took the PVA settings from the MMU1. Since this didn't work, I tried increasing the ramming from the default to about 15mm^3 of total ramming (pretty similar to PLA) but that didn't work. I also, of course, did the calibration with each type of filament, and with a fresh cut end each filament loads perfectly.

So has anyone been able to get PVA to work? What are your settings? How do you eliminate the incredibly long string or mitigate its effects on the MMU2 filament loading procedure?