If you can tie the game with 30 seconds left after being down 15 then you did good to get there. At that point, this is your last shot anyway. There is no second chance. You miss and your done. Pretty much the same thing if you miss with less than 7mins left to go down by 9. Thats what your not getting. You gain no valuable information from missing. You miss, your done. Thats the point.
And this is where you're losing some of us. You miss the tieing 2 pointer later...you might well be done (barring an on-side recovery).
You miss now...yeah, you need 2 possessions...but you're also more likely to GET two possessions.
Read that again...you are also more likely to get two more possessions. Teams up 2 scores late go ultra-conservative. They're running...you'r stacking the box. Three and outs are EASIER to achieve at that point then at any other. Teams up one score can't draw into an ultra-conservative shell. They have to convert first downs. They still pass with 7 minutes. On defense, you still need to defend the whole field...they are MUCH MUCH harder to stop. And guess what....all they need is a decent return and a first down or two and the scenario becomes more dire anyway, because a FG makes it that same 2 possession game.
At 10 minutes plus or 4 minutes minus, go for one. 10 minutes because there's too much time left. At four minutes because you're probably only getting one more possession either way so momentum and morale matter.
At 6 or 7 minutes, you go for two.
There are gray areas in between, which would be determined by things like
1. How's their running game/ how good are you at stopping it?
2. Wind/weather conditions (affecting FG possibilities for both sides)
3. Overall tone of the game (shootout vs. defensive slugfest)