The ones I know of:
Crew position on the wire. Upwind you want your crew on the mainbeam and skipper just forward of the daggerboards. You really need the sterns out of the water and dig the bows a bit. On the f16 you are bound to pitchpole upwind if you do this.
Mast rotation on the F18 you really want to have the mast more centered than on a F16. The F18 mast is much stiffer compared to the F16s; so its harder for the top to fall off in a blow.
Downwind you really want the crew or skipper out on the water to get that extra leverage. On the F16 you can get away with sailing a deeper/shorter course. You really want to heat up the F18 in order to get good speed and having the crew or skipper on the wire will give you that extra RM.