Well, there's always cheats, of course. Sobeks don't like it when a Herc suddenly starts waving around a pair of BFReds or MjolnirBeams.

(Not that I don't recommend trying to finish missions straight, but when it's not really 'your fault' that things aren't coming together...)
Checking again, one of two main things usually happens:
The Asar pulls in right alongside the Iceni(slightly ahead), and does its best to give the Iceni a constant broadside with one of its VSlashes and as many of its AA beams as it can(including at least one of the rear AAs). In this state, it'll pretty much ignore you escorting the Iceni as long as you don't make too much of an obvious nuisance of yourself. On still rarer occasions, when it jumps into this position, it will snap off a quick VSlash at the Hinton and massacre it.
The Asar still appears to the side, but over or under the Iceni and loops around, eventually ending up behind. Obviously, if it's below, it's free to unleash everything on the hapless Iceni, which might get to fire off one or two BGreen shots at the beginning. In this state, its quite happy to skewer you with AA beams and flak if you try to attack it from within 1500m. I've only seen it go over the Iceni once that I recall, but I seem to remember finishing the mission that time.