And IIR missiles are 100% effective? no. Against IRCM targets 70% at best. It is down to chance, and the engineers don’t know what they are doing cause everything is top secret, so they don’t know what they are up against any way.
However again this is down to chance, dependent on range and humidity and stuff like that that affects LDIRCM’s energy transfer onto IIR seeker.
Which means objective achieved for LDIRCM. Especially at sort of 9-10km range.
Which is hugely energetically inefficient.
Which makes HOJ the more difficult, as LDIRCM has the potential to fill that seeker.
That is 1. if it is the correct source and 2. much of the sectors would be filled out by LDIRCM and therefor HOJ would thus rely on gradient of IR signal closer to the edge to work that out. Not very accurate and this applies more so nearer the missile to LDIRCM.
That is nothing but a design, there is a reason why no one tested UV missiles, it is basically a fail safe thing much like Strela’s photocontrast mode. Also that sort of LOAL is not used anymore due to excessive need for IFF, which is modernly done predominantly with DL and not UV.