On 11/19/2020 8:35 AM, Eric Greenwell wrote:
How odd the 63:1 only occurs at the high wing loading in 21M, and not at
the minimum wing loading, where the L/D is essentially the same for the
18M and 21M wings.

Not odd at all. Reynolds number changes make a big difference especially
with tiny chord. IIRC the original Ventus 15m increased LD 2 points with
ballast, and could not change wingloading as much as modern gliders.