I have in fact put together already a scenario that works exactly like that, Daz. But what I'm actually trying to achieve - when putting it together from the player as Axis point of view - is precisely not that the Axis should be able to get into both Grandmenil and Manhay on night one without much of a fight. Because you always have to consider how very much more efficient the human player is vis a vis the AI. So if I as Axis get into Grandmenil and Manhay and camp out there on night one then, to be honest, with the historical forces available (and even if I beef up the stats for the AI allies to make them 0 fatigue and 90% aggressive with great leaders all round) the AI will not be able to get me out. Even if those two locations are its only objectives it is just not capable of concentrating the kind of force required to uproot 60 dug in panthers plus 2 Bns of panzer grenadiers. A big part of this is the reason you have mentioned - it cannot use arty in the same way that the human can. (Which is why it is 'gamey' I feel for me to be a God's eye arty observer with God-like powers of stompitude - if I limit myself to 50% then I get closer to the lesser effectiveness of the Ai in handling arty). So - in order to make this a challenge from the Axis point of view, but still within roughly historical parameters and only using the historical forces available in the historical starting positions - my aim is to set it up so that during the first night the Axis (using all the arty the player wants) cannot easily get into both Manhay and Grandmenil. Because, as people have pointed out many times, once you're in there, defending, it's much easier to hold on.
That said, the scenario I put together in the way you suggested did end up with roughly historical results -- ie, the Allies pull back, rest, attack, and after a couple of days they get Manhay and Grandmenil back. BUT, I was only able to achieve that by structuring the objectives in such a way that towards the end of the second day, the Axis focus dramatically shifts and the player is forced to leave either Grandmenil or Manhay (or both), or at least dramatically reduce the units in there, in order to get crucial exit points (without which no win) over in Awez. Otherwise the player is easily able to hold the locations as long as they want without the possibility of any serious Allied counter-attacks backed by significant arty preparations.
This is not to say that the AI is doing a very bad job. I in fact believe that the AI arty looks roughly historical. The problem, with that (the arty) and generally with aggressive attacking behaviour, is that the AI is more cautious and less efficient than a human player. BUT, the human player is generally way more aggressive, reckless (of life) and efficient than real life historical commanders. So when you try to balance things you have to take into account just how ruthless the human commander is in the game. That's what I feel, anyway.
So what I see time and again if I have most of my force dug in to Grandmenil (as Axis) is that the Allied AI will not plan a serious attack using all of the force available. Instead it will more or less surround Grandmenil and snipe away from defensive positions. But surely this is what they would have done historically with the force available against such a powerful attacking Axis force? They really don't have enough force available to mount an attack on that level of Axis power, without terrible crippling losses. And the Ai won't sanction that. But turn the tables and switch sides and I will direct every single artillery piece onto grandmenil for 6 hours, or until ammo runs out, then mount a huge attack and take all those crippling losses no probs.
One last point, rest considerations aside, the terrain to attack down into Grandmenil is all open and lethal, so to rest up in the north one night then attack the day after in broad daylight is always going to be very costly. And, in fact, the AI won't do this. Instead it will rest doing nothing for maybe a full 24 hours before doing night attacks. Sensible, but meanwhile the Axis has accumulated all those occupation points.
So it's complicated getting a challenge, but I think it is possible in these smaller scenarios. When it comes to very big scenarios I've had much less success. In from the Meuse to the Rhine, for example, and Encircling Aachen I have often seen the Axis AI sitting back in space (sometimes on objectives, sometimes not) unwilling to mount concentrated counter-attacks, I assume because the odds of heavy casualties are just too high. It seems like realistic behaviour in many ways, and it's very much more difficult to balance these big scenarios to get a more aggressive and reckless AI.
Peter