The hatch/door on the watchtower is not closeable completely if you are standing on the platform of the watchtower.

It doesn't matter if you are close or far of the hatch/door and it would not close completely.

It looks like the hitbox of the hatch/door is too large and is colliding with the player if he/she climbed up the latter and is standing on the platform.

If you climb up the latter you can close the hatch/door completely from below.

On Arland you will find these watchtowers (on the map they look like an upside down point of interest symbol) on the airfield at

grid 014-018
grid 014-023
grid 015-021
grid 015-031