Level determination *possible spoilers*

What determines what level a character will be at when they re-enter the party later on in the game.
I always try to level my characters up as much as possible before I know that I'll lose them in hopes that they will be farther up later on in the game.
Before I lose Kain the first time I try to get him to over 300 HP. I usually hope to get him back later on at around 2500 HP.
Before I lose Rydia I try to get her to 600 HP and knowing the spell Virus. I like to get her back with around 1500 and already knowing all the level 3 spells and hopefully more.
I never concentrated much on Rosa but one time I got her back and she already knew up to Cure 4 which was nice.
I like Yang to have around 1500 when I get him back in Baron. One time I had him to over 5000 HP before I lost him in the Tower of Babel. Talk about a big loss. He'll kick Edge's butt any day! He'd max out at 9999 HP before the end of the game pretty easily if you never lost him.
I never worry about Tella...in fact I always kill him to give more exp. to other members.

I plan on playing the game through the next time without stopping to level up. I wanna see if and how fast I can beat the game that way.

Anyone know what determines the level a character will be at? Does it have anything to do with what level they were at before or do you think it's based on what level other characters are at? It seems that when I get Yang back and also Kain they are always a few levels ahead of everyone else.

It all depends on what level Cecil is on. When he becomes a paladin he start on level 1 and has a lot of hp. If you kill off everyone in the party and put him in the back row, you can level him up very high, very quickly. I usually level him up to 20-23 then go back to Mysdia. You'll get Yang back at around level 25 then. In the Tower of Zot, you can do the same thing, kill off the party members, put Cecil in the back and then wait until you fight the Marrionettes and Callers. Keep the Caller alive and it'll keep summoning Marrionettes for Cecil to kill and you can get Cecil at level 50 in no time. Then when Kain, Rosa, and Rydia rejoin they'll all be around 50 or higher. It can be time consuming, but it's worth it.

Hope that helps. :D