As you can see in the video above, I’ve noticed a significant difference in scan speeds of ACM mode with Phased (aka Electronically Scanned) Array Radars and their correlations being the presence or lack of IRST systems. This does hold true for other aircraft besides the one given in the examples, you can check it for yourself (SU-30 - slower, SU-34, (upcoming f-2) - faster).
In my opinion, and according to the humble research I’ve done, I’d say it’s due to the fact that, for some reason, the acm scan speed is limited to the max sweep speed of the irst system on the aircraf. That said I’d like to know (mostly preffered from someone in contact with the devs) if this difference is supposed to be there or not?