Spotting the ball after 4th down

[BoomerSooner]

Every crew I've worked on does the same, but I've often wondered if the following logic plays out as well as the logic we use to spot as we currently do. I'm not proposing we all change how we do things, but would love to get some thoughts.

Currently the logic is that if we spot the ball with the foremost point of the ball touching a yard line, the line to gain will be achieved as long as the ball is touching that yard line, but why couldn't this entire idea be flipped. For example, the ball is spotted with the foremost tip touching the edge of the A's side of the 40 yard line for a new series. We know if the ball touches the 30 yard line, A has made the line to gain. A throws 4 incomplete passes and after the CoP, the ball is spotted at the exact same spot. On 1st down, B runs for ~10 yards and the ball is spotted such that it is laying across the 50 yard line. Assuming the ball maintains the same length tip to tip, shouldn't we know that B has not made the line to gain? On 2nd down, B runs the ball and it is spotted such that there is an inch of space between the back point of the ball and the 50 yard line. At this point we know the line to gain has been made, don't we?

Again, I'm not proposing we all start a movement to change the way we've all administered this. Just asking from a logical/mathematical perspective, does this hold up?