The e-bar set up is really cool. So is the J/99 solution.
Any sailboat makes some leeway, so the idea of toe-in is to put the windward rudder, which can't get much grip anyway, in a position that minimizes drag. The amount of leeway varies depending on all heel, speed, wind angle, etc.
I've...
I used to tune my catamaran to have the windward rudder stream water equally on each side when close hauled. I thought it was a touch faster upwind and felt better. In those days we would flip up a leeward rudder downwind if flat or sail heeled downwind too.
Now we foil as much as possible...
The interesting thing for a keelboat with twin rudders is the heel of the boat as others note.
When heeled upwind, you ideally want the windward rudder (which only will have a small portion immersed) be in line with the angle the boat is tracking. That means some toe-in.
When sailing flat...