Fixed position were never properly developed on the eastern front by the wehrmacht due to logistic shortages....not enough rail capacity, too much money spent on frivolous projects like panther, manpower shortages, and cockeyed policies instituted by the high command. Germany needed to take a reality check at the end of 41 and work on logistics rather than increasing firepower.
And your response doesnt really get to the issue facing the wehrmacht. By the latter part of '43 they could no longer fight a mobile war....not enough transport to do that effectively. Youve tried to argue in other threads that german Infantry could move 500 km in a day, but this is clearly impossible, especially with the truck and horse drawn resources available. Under conditions of engagement, except if massive losses were to be accepted, they might b able to retreat 10 km per day. if greater retreats were attempted Germany would lose huge amounts of men and material whenever they tried to move further or retreat large sections of their fronbt. The only thing they could do is fight a static line....hedgehog, quadillage, pakfront, call it what ever. The points of resistance simply sat there and resist, holding up the advance, centred around their AT defences (as Soviets say, all defence on the eastern front is an Anti-trank defence), forcing the attacker to spend time and resources to either contain them, or destroy them. The encircled, fortified and properly armed Infantry (with AT guns) defenders sat in place for as long as possible and await relief by a larger reserve of mobile forces centreed around a produceable, cheap SPG like the Stug III rather than impractical behemoths like Panther. Germans could have had 4-5 times as many Stugs as they had Panthers, giving them the ability to have the numbers needed to contain and defeat Soviet breakthroughs, and then relieve their encircled Infantry. This approach was well proven, and would have minimised losses for the defender, maximised losses for the attacker, and contained Soviet breakthroughs far more than they were by attempting to employ wholesale retreats of the entire front. Hitlers stand fast orders, in a perverted way made some sense. What was missing was that his Infantry was not properly entrenched, lacked sufficient AT defences, and the mobile forces continued to be equipped with inadequate numbers of turreted tanks 9an inherently offensive weapon). The force structure and the preparations needed to be chaged to make this policy workable.
Contrary to what you might think or say otherwise, Germany could no longer afford to think and fight fully mobile wars by 1943-4. They didnt have the transport. Big sweeping movements of the army would always cause massive losses because german Infantry could not move fast enough, and there is nothing so vulnerable as Infantry caught exposed and poorly dug in or not dug in at all.
And for the record, fortifications could have worked if constructed properly, or at least Manstein thought so. As I said, Germany never got the chance to develop these sorts of fixed line defences properly, even if they occupied the ground for an extended period. Hitler in the first instance forbade their construction, because he thought the army would fight less hard if they had fixed defences to fall back to. in the second instance, Germany never poured the resources into building proper fixed line defences. Manstein rightly pointed out that the correct way to build proper defences was not to have a line at all, rather a series of strong points behind a natural obstacle, like a river or a desert....leave your opponent exposed, and channelise their lines of advance.
Saying that defences didnt work, on the eastern front because of the length of the front, is clearly a nonsense. Your assertions about fixed lines not being effective are clearly not views shared by some very prominent and successful generals from both sides, including Manstein, Model and Zhukov. There were many others. And there are many examples of such tactics being eminently successful, but you have to look at the Russian side of the fence to see that evidence. Even where fixed lines were eventually defeated, such as at Odessa and Sevastopol, they were successful in delaying the attacker significantly. What was missing in those instances was an effective counterattack force. In those instances where an effective counterattack force did exist, fixed line defences were essential to ultimate victory. Suggest you go back and have a look at how the russians won at Kursak and in front of Moscow, unless of course you subscribe to the view that it was all the result of the weather that the city was not taken and that in the case of Kursk you give me a Kurfurst style answer and try and argue that the germans weree successful and simply didnt need to attack anymore.