Also, our insurance states that there will be an instructor "on the field",
with solo students, but does that mean, feet on ground?

My club http://www.soargbsc.org is insured by Costello and has the same
statement. We asked for a clarification and were informed that the
instructor has to be on the field to approve the flight. The instructor
is then free to perform other tasks - including flying his own glider
for fun (what a concept :-).

Tony V