I'll offer the following carrots to munch on:
1. If you need to "preemptively employ countermoves, after the covering force crosses the battle handover line, to reinforce against or block the enemy and prevent him from finding the path of least resistance," (to paraphrase your first statement) then you've probably set your battle handover line in the wrong place. If I was planning a defensive fight, I would not want a "break" in contact between the covering force and the main defensive force during the defensive battle.
2. If you have "12 different counterattack tasks on your countermoves matrix," (to paraphrase your next statement) then you're probably mishandling your reserve. The last thing you want to do is fritter it away piece meal reacting to every enemy action considered a threat. "Firebase positions and attack positions" are things you deal with through your direct and indirect fire plans, not by committing your reserve.
3. The way you frame your argument seems to argue that an area defence (as portrayed in Land Ops) is too reactive in blocking/reinforcing and waiting for the big counterattack at the end. If I read it right, you are arguing for "using offensive action in the defence" and that constant counter-movement (for lack of a better term) would be implicit in an "offensive defence." Are you just indicating a preference for mobile defence over area defence? While preference is fine, means and circumstances may not give you the choice. However, the scenario you appear to describe is common, especially in theatres with a low density of forces - just look up some German defensive battles on the Eastern Front. However, in these cases both tactical and operational reserves are still maintained as the defender conducts his mobile defence.
4. The primary reason I would argue that you wish to avoid committing your reserve early (in either a mobile or an area defence) is that you tip your hand. This goes back to Old Dead Carl and the very reason we find ourselves on the defence in the first place. We are on the defence because something is preventing us from going to the offence. That something is probably a correlation of forces, or we'd probably just take to the offence ourselves.
The defensive concept is parrying a blow, the characteristic, awaiting the blow, the object, preservation. I need the enemy to wear himself down, commit his reserve, limit his freedom of action, and in doing so culminate so I can then act to take the initiative. This is when I introduce my reserve, for if I introduce it earlier, I'm probably doing what the enemy is looking for - he'll then commit his reserve to run my committed forces over and achieve breakthrough/breakout. In all higher level exercises I've been exposed to, we try to get the defending enemy to commit his reserves so we can destroy them and take advantage of the loss of freedom of action he now faces. If he commits them early, so much the better.
In the end, I'll again offer my opinion that the Canadian doctrine is a bit simplistic due to our institutional unfamiliarity with sustained defensive operations and the relatively low level that it concerns itself with. It's not in our heritage or collective memory. If you want a good synopsis of the state of the art with all the nuances of different defensive approaches, here's a
good read.