When you extend a surface, IV fills in a distance value and previews the extension. Where does that default value come from ? We used to think it was the maximum distance that Inventor could reliably extend but that's clearly not the case.
In a part we've got, IV defaults to .500" and hitting OK completes the feature. In a 2D drawing, dimensioning the extension does result in .500". If I extend the opposite side, it again defaults to .500" but the preview and the result clearly aren't the same as the first extension. In the 2D drawing, it dimensions to .07". For the side with the actual extension distance of .07", changing the value from .50 up to over 1" does nothing to the preview and the feature will complete, but the distance still remains .07". If I try 1.25", for example, it fails. It previews -- at a shorter extension than when .50" is the filled-in value -- but still fails.
By the way, using "Stretch" is not being considered.