Do character positions at the table matter?

As best as I can tell, absolute position doesn't matter, but relative position does.

By that, I mean that while it doesn't matter if your tank is on the right end or the left end, the tank should still be on the end with someone who can take a few hits next to him, because of enemy attacks which hit the target and anyone adjacent to them. By placing the tank on the end, the monster will waste one third of a Cleave-style attack if it targets the most likely target. And by placing a high-hp ally next to him, the spillover isn't so bad.

As for the necromancer, he buffs a friendly target and both adjacent allies, so you want to group the characters who can benefit the most.