The rudders are set up the same as any rudder system. That is to balance the helm there has to be a small proportion of the leading edge of the blade in front of the pivot point line of the rudder stocks to keep the helm “load” as neutral and light as possible. If that percentage is too much the helm will “dart”. If that percentage is way too much, as you turn (either up or down) the tiller will be ripped out of your hands. If there is too little percentage in front of the pivot, the helm will be “heavy” both pointing up or down (this is not “weather helm” which has entirely different causes) If the rudders “trail” fully behind the pivot line, the helm will be so heavy (with extreme trailing) that the boat will be almost impossible to steer, so assuming that the helm “balance” is correct, then the foils are positioned, as I said earlier, parallel to the water surface.
When we made these foiled rudders, we moulded new stocks that let the rudders be pulled up or down vertically in the stocks, (as opposed to a “kick up” system) but with an angle that slightly “tucks” them forward under the transom to balance the helm, this allows us to position the height of the rudders at any level that we like to allow for launching, retrieving, sailing in deep water or in shallow, the rudders are placed at the appropriate height at the time and are simply “pinned” there. This was the simplest and most cost effective way of incorporating T foils. With the rudders fully up on the beach, they are completely clear of the sand.
As far as I have been able to ascertain at this time, too have an effective T foil system on a kick up system the foils would have to be automatically mechanically articulated so that as the rudder swings through it’s arc, the foils will pivot and still maintain their parallel attitude to the water. This is not a great problem of design, but it would make for a rather complex mechanical solution, not to mention, expensive.
The angle of the foils to the angle of the rudder will be determined by the rudder position, which as you say RICH, is when you have the rudder in the correct position on the boat to balance (or “tune”) the helm, then set the T foils parallel to the water surface.
On any other plane, the Foils can be “raked” backwards, forwards, or with dihedral either up or down, or they can be curved. Those alternatives mainly depend on personal preference.
The T foils themselves seem to have no effect on the balance of the helm at all; their only noticeable effect is in greatly reducing the pitch of the boat.