In response, further modifications to the design were made and three additional prototypes were manufactured, labelled 30.19 (for tests on the ground), 30.20 (for in-flight tests) and 30.21 (as a reserve airframe).
Podjęto więc prace nad modyfikacją myśliwca, tworząc trzy kolejne prototypy oznaczone 30.19 (do testów na ziemi), 30.20 (do testów w locie) oraz 30.21 (jako rezerwowy).