The rules say armies with Tactical Doctrine can have 2 free ambushes. Is this over and above the ambushes you can use from your Reserve Pool as outlined on p.61?
You can only Ambush (even from Reserve) if you have Ambush assets (either free or Purchased).
Troops in Reserve are deployed separately from an actual Ambush. Following a successful CV roll by the Command unit (to which the units in Reserve are attached) these units can then be deployed within the proscribed distance of the Command unit. This is not an Ambush and so none of the special Ambush rules apply to it.
It just represents units that have been attached to that Command unit and are called-up for deployment.
Ambushes don't need a successful Command roll to be activated - they can triggered by enemy activity, although you can use a Command roll to activate them if you so desire.
Hope that makes sense?
Mark