I know what I think the answer is, but let me see if I can prove it.
If you chose to change the spell you are the new controller (not the caster).
So then each target would be set based off the casters location.
You may chose at that time to pay more than what was spent thus increasing the range.
after reading those this should all be easier to understand.
Remember teleport has 2 targets
1: the zone you are sending something to
2: the creature being sent
Thus a max of 4 zone is possible
so if something was going to be sent 2 zones and everything was perfect you could send it four zone instead but you would pay the extra 6 mana
Is that what you you needed?