Afar as i could read up in the forum, the ai seems to magically know your spi at all times. Broadcast on or off doesn't matter, and sending your spi via message doesn't have any meaning, the ai still targets your current spi when you give the actual attack order via radio. So it seems not to be possible to sort of give your wingman and second element spi coordinates via message, then lock up a third target yourself and then give the final attack order via radio. The ai "forgot" the spi message already and all attack at your current spi. Anyway, its just a minor immersion and tactical breaker.