In RoR, I believe this is a bug - and a nasty one!....
Every time you order a high-range unit (like an HCAT) to fire and that order involves the unit positioning itself, the AI does excess movement before firing, thus creating a fatal situation for a slow unit.
This is visible and annoying as hell - against Towers, Helepolis and other Cats - but most of all against ships (since they are normally massed).
It's incredibly mean, you just can't attack other siege or missile units when you move. My experience shows that it is now the opposite of AoE. In AoE, Siege were glorious attacking. Now they must be there, awaiting ... or else do foolish things by themselves.