Unable to build portal on first floor of base

I wanted to place a crude portal (card playing machine) on the bottom floor of my base (on Bhutan foundation) but it wouldn't allow it. It would allow it in one area near the front door. So I placed it on the 2nd floor successfully. However, I cannot place any work stations in the area below the portal. It probably has something to do with the invisible foundation block attached to the bottom of the crude portal?