It seems to be the case Rolf, that by stopping the mast movement back and forth from a pitching hull, the airflow across the sail is obviously more stable and constant. When the mast "rocks" back and forth the airflow across the sail, when the mast moves forward, will effectively be faster, but as the mast moves backwards the effective airflow is much slower even to the point, particularly in lighter conditions, of "stalling" the sail until the mast once again moves forward. The more constant and even that the sail moves through the air the better. This must also apply to the hull movement through the water. We all know that to jump about on a cat will detrimentally affect its performance, so to stop pitching and “stabilise” the extremes of the hull movement must be “all good”.
I, like most others, initially thought of T foils as being a simple addition to limit or stop the potential of “pitch polling” under extreme conditions or with the spinnaker “bear away”, but I am starting to feel that the “all round” beneficial effects of T foils may be far greater than just that of a “pitch pole” limiter.
PS I am talking here more about the "natural" movement of the cat following the wave surface of the water as opposed to what we consider as a more violet rapid "Hobby horsing", although the stabilsing effect is the same for both conditions.