Hi Rob,
Maybe a mis-communication, what I meant was some very tight reaches, ie as high as you could go in those conditions without capsizing, crew on the wire. What we`ve found with the Mozzie is that if you`re 2 out on the wire with the kite up, you`re reaching too high for a spinnaker, and a sloop without spinnaker will go past you, since 90% of the force in your spinnaker is now trying to push you sideways, and only 10% forwards. When I said "tight reaches" I meant relative to apparent wind. We had to clear a shallow point in the course, sometimes you had to take the kite down. It was probably slightly off a beam reach, making it too high to sail in those conditions. Sorry if I misled you into thinking we could close reach with kite up in 12-20 knots !
The cut of your spinnaker has a lot to do with it, more fullness in the luff will cause it to collapse earlier than a flatter cut. My kite was fuller in the luff, and I could`nt reach as tight as the rest of the guys, so I had the luff re-cut, much better now.
21sqm .... ARE YOU NUTS ?????
Our spinnaker is only 13sqm (projected area), probably about 15sqm of cloth (not sure how you measure spinnaker areas, flat or projected ?)

Cheers
Steve