Oliver Moffatt writes:

Excellent and experienced aerotow pilots I have spoken to,
including multiple British champions and the UK Moyes importer, tell me that 1/3
to 1/2 VG is essential for a normal-weight pilot on an RX, with more VG possibly
required for a pilot lighter in the weight range. I am light on this glider and
I typically use just over 1/2 VG, which works very well.

Steve Pearson writes:

1/2 VG is recommended for aerotowing all Wills Wing gliders
configured with VG systems. Towing at less that 50% VG is more difficult because
the pitch pressure can be excessively high and that in turn contributes to PIO.