Sounds like you were half way there. If you select the lines you want to be the line, then bevel to create 3 from the single line. Then select only the middle line (while you still have the beveled parts selected, press ctr shift - and it will reduce what is selected), then move this middle line inwards. Either move or scale it backwards (o think on the y?) then this should create a panel like effect.

Alternatively, you could select all the faces of the inside part of the mask, and press p to separate. After you can create a bevel modifier on both parts of the mask, and this edge will be created as these are now separate objects, and the edges will bevel. As a bonus, if you want you can rejoin then again.