Celebrim
Legend
Isn't what you are doing essentially the same thing. You are framing the scene in such a way as there will be auto success? What does it matter if your pre-framing of the scene includes a "safe hiding spot" due to distance and location or a "safe hiding spot" due to being able to get close enough by sheer luck and chance?
Is that actually a meaningful distinction when you really sit down and think about it?
There is a small distinction but it is meaningful and to really see how meaningful it is I'm going to first reach for exaggeration.
Suppose that I create a Tomb of Horrors knock off, and I have in the dungeon a door which when opened is some sort of nigh inescapable death trap. The door, the corridor leading up to it, and the effects of the trap are well described prior to play.
Now suppose that I'm running a dungeon and the players open a door and I decide that the opening of this door triggers a nigh inescapable death trap which I invent on the fly.
Do you see that there is a subtle difference?
What it comes down to is that as a GM you have basically infinite resources. You can do anything you want. But if you fix those resources in place prior to the beginning of the game, and hold yourself to them as a restriction on what happens, then you lose perfect control over the game. As GM, you need to hold yourself to some finite amount of resources. You can weight the situation heavily towards favored outcomes - and indeed every module ever written is weighted toward the outcome of party success to one extent or another - and still be running a fair game in that you are sharing agency with the players. But if you don't limit yourself in your resources and wait until the game starts to decide what you want to have happen, then you are putting yourself in a position where it is inevitable that you have both access to your infinite resources and you are biased by the current game state because you know what that game state is so that you basically have to admit you are the only person with any real agency at the table.