Infiniti2000 said:
If the save is irrelevant, explain why you choose one effect over the other.
Simple.
The movement portion of the spell is different and distinct than the initial entangle condition which prevents movement.
If you start outside of the Web, you are not entangled at all. You are merely moving through the Web.
If you start inside of the Web, it does not matter if you missed your save or not. You cannot move through it without making a Str or Escape Artist check each round. The save merely helps determine when you can do that (either immediately, or after you make Str or Escape Artist check).
Both of these are movement. Both use the Web movement rules.
You are adding a "when you enter the Web, the spell is now cast on you" rule that does not seem appropriate. You are moving when you enter a Web, so you use the movement in Web rule. You do not use the "within the area when it was cast" rule because a) that did not happen to you, and b) you are moving.
In other words, in the case that you are in the Web and make the save and in the case that you are outside the Web, you can move through the web on the next round by making the appropriate check because in neither of these cases are you both entangled and prevented from moving.
Moving through the Web does not force a new saving throw, regardless of how you managed to start moving through the Web. The character moving from outside the web is not forced to make a saving throw no more than the character moving inside it is (once he starts moving). This would be no different than a character who leaves the Web and then goes back in. He too is only moving and follows the Web movement rules.