Nick - good question. The elevons were not hidden at high AoA (no elevators, no T-tail issue) but high alpha longitudinal stability was an issue in early development, one of the fixes were the moustache strakes you see at the front - they help energise the wing vorteces and improve rudder authority at high AoA. Apparently. Well that's what they told us at ground school - the result was that right up to limiting AoA all flight controls were effective, including the potentially blanked-off rudder. IIRC the stick-shake was at about 16 degrees which left about 3 degrees slack above approach AoA and it all worked just fine in that environment.