I want a Zone of Control for fleets.

It might feel wrong since the space is so big that a fleet shouldn´t be able to block movement in a tile where they aren´t. But this is how argue for it.
The turn based game is a way of bringing some kind of structure to movement that happens in real time. But in real time the movement of fleets would have to react or at least consider enemy fleets movements. Therefore you could consider in a turned based game that the end tile for the fleet would be a "Schrödingers fleet". It could be there but it could also be in the squares next to it depending on how it reacted to the movement of the enemy fleets.

The ZOC could be adaptive to the movement range of the fleet, range of sight and some new special equipment. I haven´t analyzed how the change would impact on the game, but I think most of the changes I can think of would be positive for the strategic part of the game.