2x2x2 Maelstrom.  My ai allie has amassed a considerable fleet with the intention of teaming up with me for an all out on the enemy ai's home world. 

Unfortunately the world we are massing at used to belong to the enemy ai and was once in its trade lane.  Every time a single trade ship enters the grav well every ship of the ai's breaks formation to give chase.  Every carrier, 20+ discharges all its strike craft.  4 Cap ships, 20 Hosikos, 3 dozen LRMs, etc. etc.  Ofcourse the strike craft destroy it in a single pass.  Then the ai attempts to under take reforming its fleet at the edge up the grav well to begin the invaision.

Ofcourse you know what comes next, before it can jump, another trade ship enters the grav well.  Rinse and repeat.  This happens three times.  With enough trade ships, the ai is virtually paralyzed, which maybe explains why they don't go for it.  They don't push their advantage.  They can't follow up their wins when trade ships enter the grav well. 

Keeping a supply of scouts, sending one at a time into the grav well of the ai would likely accomplish the same thing, disrupting his entire smack down fleet and imprisoning his fleet maybe indefinately.

I would suggest the ai ignore these ships, or any single ship other than a siege frigate.  The benefit of destroying the ship would have to be offset by its inabilty to maintain offensive momentum.