I want to achieve a uniform bevel on the top surface of my model as shown in the first image below, but the bevel is spoiled by 2 'extra edges' joining the top edge loops (image 2).
No matter what method I use (see other images), blender always leave behind the 2 extra edges.
Why are the 2 edges there, can I get rid of them, or how otherwise can I achieve the uniform bevel?
NB1: I have tried Dissolve Edges, but once you get down to 2, blender says 'Invalid boundary region to join faces'.
NB2: I can't use mirror modifier because this is a simplified example of my more complex model.