I had no luck making it invisible frame or 0 thickness frame, so I usually give that frame a 1/4" to 1/2" thickness for the threshold. If it has no threshold, 1/64".
After you adjust the thickness, you need to adjust the adjacent vertical frames intersection priorities to make them join properly.
ArchiCAD 25 & 24 USA
Windows 10 x64
Since ArchiCAD 9