The reason I started this was that the tiller (when slipped an inch back or so) rubs the cover of the tank.
Perhaps the tiller is bent?
The receptor on the rudder stock is pointing slightly upward. If the tiller is straight it should pass well over the hatch regardless how deep it sits in the receptor.
With the tiller taken from the rudder stock, look along its length with an eye close to one of the ends. Any bent should then be obvious. If it is bent just bend it back carefully until it is straight again. A Wayfarer tiller (wood or aluminium) should be straight (except for the occasional S-shaped ones some cruisers specially made to be able to open the hatch while sailing).