Nice idea but you should edit the positions so that they don't look like solvable puzzles. They are all just static positions. I thought they were stuck. (While that would be cool, I realize how much work that would be.)
After figuring that out, I finally got back to your question about how far away the black king has to be for white to break through successfully.
I recently played a pawn ending in bullet thinking it was a dead draw. It actually was a drawn position, but I didn't think about my opponents only pawn break. When he makes that pawn break my king must be close enough and mindlessly I wasted some tempos by moving my king back and fourth on the other side of the board. After the game I thought it would be a good exercise to see how close my king needed to be to be able to draw. I think I solved the exercise and thought I should share it in a forum. So the exercise is to find out which of these positions is won for white and which are drawn (White to move in all positions). The only difference between the positions is the placement of the black king.
note: The diagrams below are static positions, not puzzles