Did your sensor rise above the water just before the foils rose to the surface? If so, this is common on the leward foil. It is called sensor rising. It is caused by the downforce on the leward foil in combination with the geometry of the foil control system. . It can usually be compensate/elliminated by lengthening the shock absorber adjustment and thus creating more downforce n the snesor.
15 to 18 mph should be Ok for 2 people.
HC 18 Magnum