How can I create a corner box window?

Can anyone advise on how to create a corner box window in X4?
It is raised off the ground and wraps around the corner. I've got a box window on each wall in plan, but cannot get them to meet/overlap at the outside corner.
Thanks,
Erin

There might be a better way, but I just draw the walls, use invisible walls to make a little "room" there with a higher floor level, put the windows in, drag the bottoms of the walls up as necessary, edit the foundation as necessary and then just use p-line solids or other means of filling in the gaps (not shown for clarity).

Thank you for the reply Sutcac,
I somehow knew it wouldn't be a simple matter of manipulating those box windows. I appreciate your set-by-step suggestion which seems pretty easy. Plus the plan drawing looks more accurate.
Thanks
Erin