I think it is interesting to look at what types of glider have been involved in
aerotow upsets in the past.

Most of the incidents/accidents cited here have been in older generation
gliders with low wingloadings and stalling speeds. They have a natural tendency
to want to rear up behind the tug and the aerotow is generally flown with quite
a large amount of forward stick, possibly outside the trim range.

Compare this with the later high wingloading glass gliders, especially when
flown fully ballasted. Unless the tug accelerates to 70Kts or so you are left
dangling below, trying to get out of the slipstream.

I find the most worrying thing about towing from a belly/winch hook is the
possibility of a back release at an awkward height. When I do a long tow I
disable the back release.

I find towing off the rear hook more comfortable in some gliders, as the nose
doesn't get dragged into the turn so much. I have a '27 and the nose hook is a
bit of an abortion so I don't use it unless I have to (slope, crosswinds etc.)

As a tug pilot I would be quite happy with someone in a modern glider behind
me, towing on the belly hook, as long as they were trained to aerotow properly
and paid attention to what they were doing. If in doubt, pull the release!

Anyone who has aerotowed in gliders from the 60's or before, using modern tugs
and their higher speeds, will know how 'on the limit' the whole thing feels and
what a relief it is to come off tow. Compare that to modern heavy machines
where you have a large margin of control.

To summarise my opinion: In modern gliders the hook position is almost
irrelevant when discussing the possibility of an aerotow upset - the main
factor is the competence of the guy on the back and how much concentration he
has on the task in hand.