Do the two scalar units have to be on the same plane?

What you indicated you wish to do, is how mine is currently set up. Across the house, top floor to bottom floor. I did point the back of the lids towards the other corner of the house, but I did not bother to angle them to account for the elevation.

There are really no hard-fast rules. Do try to avoid metal, but you don’t have to go crazy trying to. My wire makes a hard right turn to go down the stairs, which has an iron railing. In fact, my wire runs past a lot of metal objects. I did not wrap my wire around them though. I did have a coil of wire when I first tested the configuration (didn’t cut the wire off the spool), and it still tuned. It tuned a lot easier once I trimmed the extra cable off.

Follow-up:

For more details, please check this link:
https://www.facebook.com/groups/spooky2scalar/permalink/924410924799133/