In article 4034d5a6$1@darkstar, Mark James Boyd wrote:

What is this airspeed? Well, it varies with weight,
and the amount of ground effect. So it is a little
bit experimental. Somewhere between 2/3 published min sink
and min sink is what I have seen.

I've noticed ground effect is very subtly different
for low vs. high wing as well. I think this is one more
reason why high wing cessnas and 2-33's are a little
easier to land than mid/low wing Pipers or Blanik/Grob 103s.

It is a little subtle, but the lower wings really do seem
to get more dramatic ground effect those last few feet,
and this dynamic interaction on T/O and landing
seems more pronounced than in a high wing.