How to calculate movement within an area

Related: How does the UA Tunnel Fighter fighting style's reaction attack interact with the Sentinel feat's speed-reduction effect?

The Tunnel Fighter feat from UA has the following wording:

As a bonus action, you can enter a defensive stance that lasts until the start of your next turn. While in your defensive stance, you can make opportunity attacks without using your reaction, and you can use your reaction to make a melee attack against a creature that moves more than 5 feet while within your reach.

What exactly is meant by moving "more" than 5 feet?

Would either of the two following paths be considered moving "more than 5 feet", assuming the player was holding a weapon with reach?

  • Path 1: Enter range, move 5 feet, exit range
  • Path 2: Enter range, move another 5 feet within range
  • Path 3: Enter range, immediately exit range
┌───┬───┬───┰───┬───┐ │MAX-RANGE->┃   │   │ ├───┼───┼───╂───┼───┤ │   │   │ .------P_1│ ├───┼───┼─|─╂───┼───┤ │ME │   │ `-->F │   │ ├───┼───┼───╂───┼───┤ │   │ F <--------P_2│ ├───┼───┼───╂───┼───┤ │   │   │ .------P_3│ ┝━━━┿━━━┿━|━╃───┼───┤ │   │   │ F │   │   │ └───┴───┴───┴───┴───┘ 

PURELY looking at the diagram and adding up the lengths of the lines, you could calculate the sum of lines WITHIN my range as being:

  • Path 1: 2.5 + 5 + 2.5 = 10
  • Path 2: 2.5 + 5 = 7.5
  • Path 3: 2.5 + 2.5 = 5

But I don’t know if this is strictly correct. I suspect that partial values may only be calculated before, or after, movement.

If movement is calculated before the step is taken, then stepping into my reach won’t count as movement within my reach, but stepping out will count as 5 feet. This makes Path 2 safe to travel.

If movement is calculated after the step is taken, then stepping into my reach will count as moving 5 feet within my reach, but stepping out won’t count as any. This makes Path 2 dangerous.

If movement is only calculated when it is entirely (start+finish) within reach, then all paths are safe.

There’s a lot of different ways to spin this. Is there any official ruling on how to calculate movement within an area?