I've noticed that the Improved Liches only do their "Come to Me" Teleport Field ability if you cast spells: My Cavalier was playing hide-and-seek with Deirex for quite a while, but as I ducked into the side bedroom for the Nth time I decided, "Hey, you know, I'm getting sick of taking all these Flame Arrows." So I used my Book of Infinite Spells (Spell Turning), and then ala-kazaam, everybody in my party could reach out & touch someone. I had to hustle to get them back out of range.

Of course, Thieves setting Traps also count as spells to Improved Liches.

Not necessarily. You have to be a certain distance from the Lich for a pre-arranged amount of time before the Lich uses Telly Field. Trust me on this one; my Archer can attest, after try to play hit-and-run with those damn bodyguards the Liches in the temple have.