I guess both parties are moved "simulataneously". So there would be a Meeting Engagement exact in the middle.
I also thought about a early counter-attack but for now we have to think of our probing first. But of course the possibility of a counter-attack over the bridges has some effects of our turn 1 positions in the rear. But if we see that the bridges are mined (what I expect) in turn 1 (one of the most important task for the probing) then we cut out the possibility of a counter-attack....
The different units have different movement allowances, to represent the different speeds at which they move in a given battle turn.
So, if they are the same unit type, with the same movement allowances, yep they meet (or should!) "in the middle" ...
But if they are different unit types (and made up of different units each side, and so move at the speed / allowance of the "slowest"??), presumably the meeting point would move towards the "slower" unit / force, to reflect the different movement allowances / speed?
I am presuming something like, each unit moves the same proportion of its total movement allowance in turn, until they either each their destination or a "meeting" occurs ...
So, any unit must move a minimum of one square each step, as that is the minimum "resolution" of the map: so a unit with an allowance of 4 squares uses 25% of its allowance to move one square. Therefore a unit with an allowance of 12 squares gets to move 3 squares in one "step". After all units have moved one "step", another "step" is done by any units with more move instructions, and so on until all is resolved ...??