No, as far as I know, acquisition range only determines range at which units acquire a target. This applies to both melee and ranged units.
The "Combat - Attack - Range" is the maximum range at which unit will initiate attack.
The "Combat - Attack - Range Motion Buffer" is the maximum additional distance beyond "Combat - Attack - Range" before attack gets cancelled.
For example Rifleman has:
- acquisition range: 600
- attack range: 400
- range motion buffer: 250
So Rifleman will notice an enemy at 600 range and runs towards that enemy until he is within 400 attack range. Then he initiates attack.
The target is running away from Rifleman and Rifleman himself has to stand when attacking, so the distance is now greater than 400.
But if Rifleman reaches his damage point and the target is still within 650 distance from him (400 attack range + 250 motion buffer), then Rifleman will successfully shoot at the target. If distance is greater than 650 (i.e. Warden that Blinks away), then Rifleman cancels his attack.