You might have to treat the sashing around the mega block as a very long and narrow block and most likely will have to assemble the top on Layer 2 where your blocks are free floating. I'd have to see the image you were original using to give you a better idea of where to go. EQ is great, but some of the things are not totally intuitive or well documented I've found.
Just informational, but there is a dedicated EQ section on the board just for questions like this one :-)
Diana