You may want to experiment with having your medium cruisers just ahead of your Star Destroyers. At least when fighting against the computer, the first thing they generally send at you is the corvettes. ISDs while the most powerful ship in the game, are not able to target the smallest capital ships as well as medium cruisers. If you have your Vic's out front, they'll make short work of the Corvettes faster than the Star Destroyers. Once the smaller ships are dispatched have your mediums fall back a little and let your larger capital ships pull front and center to engage their own medium cruisers.
Just an observation
Having your ISDs out front doesn't hurt at all, since Vettes aren't a threat to them until the shields are down. (I've noticed the smaller faster firing craft are very effective at eradicating unshielded hardpoints) it just seems a more efficient to have the medium cruisers engage the ships they're meant to destroy.