Hi guys, just to add my two cents worth and based solely on a Storck size 51, I have personally not found fitting into that geometry difficult and I had been transferring my geometry from Cervelo (S5 size 51) and Pinarello (Dogma Size 51.5) - the latter being more "conventional" I guess. In fact, the Cervelo was more difficult to fit as the head tube was too high to correct unless I used a negative stem.
My LBS who does RETUL fits for a few Stocks already have not found any problems fitting people out for optimal power and angles - though they are predominantly the smaller sizes. Some variations in spacers and stem length were needed compared to "conventional" geometry - and this has to be expected because the geometries are just different but I don't think I will go as far as to say who is right or who is wrong.
In my case for example, I had to add 10mm (I am still ok up to a further 5mm) on spacer height to increase stack and subtract 10mm from my "normal" 120mm stem length to achieve an optimal fit - variations which are not too extreme I guess. I did use a zero setback post though but that was because it gave me a better open hip angle on the drops and an overall better balance on the bike on the drops. A normal setback post would have worked too (perhaps better for a climbing build) but I would be more upright, with added spacers and seated further back while preserving my optimal body-knee hip angle. As the terrain is mostly flat in Singapore, the zero setback was more optimal in my case for flat runs. I guess it differs from rider to rider and course to course but generally no issues in fitting with regards to the size 51.
The most important thing to me at the end of the day is that the bike must feel balanced with proper power transfer and that proper fit is not difficult to achieve on a Storck. However, I could be generalising as I am basing this feedback on a Storck size 51 and maybe my body geometry is within a "Storck geometry acceptable range".
I am no expert on how seat tube / head tube angles / rake / chainstay length / BB height /rake / stack and indeed even material differences ALL interact to affect handling but intuitively I would think that we cannot isolate a few of these factors and conclude that Storck's geometry does not work. From the literature and having the opportunity to hear from one of Markus' talks, Storck uses proportional tubing (in addition to asymmetric) which means virtually every bike size of the same model is a different bike - the material thickness, carbon layout etc are different for different sizes. Maybe this is why Storcks have a premium price - the cost must be high too
Theoretically, this results in better matching of material and carbon layout design ("hidden" factors but very real) for different rider sizes so that smaller riders do not get a stiffer frame than required and bigger riders do not get an overly soft frame.
I am speculating here (don't flame me) but this difference in internal design may account for why zero setback posts, which are generally less forgiving, can match Storcks better (apart from the shorter reach it translates to) that so many people have reported and perhaps maybe less rake is required (this is out of my league I concede). Yes, this still does not explain the reach and stack differences on Storcks but my point is that judging Storck's overall handling on geometry alone may not give the full picture. Also yes, fit issues are more remote from material and internal design but I have also seen various fit experts e.g., John Cobb advocating a lower stack-longer reach with slightly more forward positioning not to mimic a TT position per se but to preserve a more or less same hip angle (which affects power and breathing) compared to the more traditional further back-higher stack-shorter reach geometry. His logic is simple - the hip angles are the same in either positions but more aero in the former which seems to describe the Storck geometry better. I know there will be people who will disagree but this is just one school of thought that maybe Storck bikes share the same idea.
I think on-road tests are ultimately important to conclude whatever works or not. After all, there are far more permutations of body geometries than Storck geometries. You have to ride the talk to judge or better still, talk the ride.
Again just sharing some of the stuff I have read and providing real feedback from my experience with the Storck geometry (and on a size 51) so far.