Obviously, only when starting a real webApp do the problems present themselves.
The "real" webApp (so simple it even souldn't be called real) didn't have any header or footer. And neither any "content" as defined on my previous example. All content were some absolute positioned divs, and a background-image scaled to 100% of both width and height (that means that at least in one orientation it was distorted, but it was so by design).
Any of the hacks which worked for my test app produces unsuccessful results, but as I didn't want to place any empty placeholder divs, was short on time, and the webApp was designed to be added to the home screen and using all screen space, I left it as is, without hiding the navigation bar when in browser mode.
Some day I'll try to find some more answers about successfull iPhone screen size detection...
