Hi Jacko,
If you think about an AESA as a Raster type scan but using a pencil beam - so a thinner elongated main lobe than a Mech Scan - with the ability to scan at a very high rate you get the benefit of more power in a dense lobe. (Although the AESA May actually use s pseudo random scan in practice).
AESA can also have a better signal to noise ratio than other systems.
Contributing to a longer range track is also the ability of the radar set to achieve multiple inputs by prioritising the scan around an initial hit. As discussed before there is no real loss in overall performance as the scan rate is so high. Rather than waiting for the next re-visit of the main lobe in two, four (or so) scans time - the set scans around the first detection and therefore track builds where a mech scan may simply not have the updates to meet its own ‘threshold’ for displaying a track.