Neither the Mk3 or 3A HF aerials are attached to the fin, there is a mast on the port side just forward of the tail fold, the aerial then goes to a mast high up on the fuselage and just below the radome and from there, on the Mk3 it goes to a mast on the top of the sponson, on the Mk3A vertically down to the mast. Your drawing appears to be a Mk3 in which case the mast on the sponson would just be visible.