This catcher is properly setup as not to be guilty of obstruction.
He has given the runner an unimpeded path to the base, and made part of the base available to be touched by the runner.
The area to the left of the red line is a path to the base, left for the runner.
From this position the fielder may move into the area to the left of the red line, IF, in the umpires judgment, the fielder must move to that position as a necessary act in order to glove the ball. The ball must be in-flight and near to the fielder before he may move into the runner's path.
The catcher above is also in a legal position. The runner has an unimpeded path and access to the base.
The catcher above will be guilty of obstruction unless he gets possession of the ball, before the runner arrives at this space.
The catcher above may be guilty of obstruction. It would depend on the runner's path to the base.
These are examples of a first baseman legally awaiting a pick-off throw from the pitcher. The fielder may not move into the runner's path, unless he must do so as an act necessary to glove the ball.
The first baseman above, will be guilty of obstruction if the runner is impeded before the ball is in the glove.