These only state that the heighest point of the mainsail is used to determine the "mainsail hoist height" and this may not be further above the mainbeam then 8.5 mtr. Of course the luff length is also limited to max 8.1 mtr and it must be a "soft sail". These are all the rules that govern the F16 mainsails.

In short, you can pretty much have whatever head you want as long as no part of it is higher up then 8.5 mtr relative to the mainbeam. So an upward angling head will say the top corner of the mainsail (near the mast) be closer to the mainbeam then 8.5 mtr. That is the payback is you want a 100 degree top corner angle.

Wouter