If after connection, levels in external corners adjoin not densely, follows any firm and smooth subject with effort to walk along the existing crack. Tree edges thus will be crumpled inside and will close an undesirable crack. To such, on the first a look, apparently, it is low to a technological way often professional joiners resort even:
Often at installation of the last fourth level in a frame, it appears that it is too short exactly to close perimeter. In this case follows: first, to cut a little an inner edge of a short level, and, secondly, to cut the outer edges of other three levels on the same size. The frame after that will become a little thinner, than you planned, but equal: