Thanks! Finally, I figured it out. Positioning is not too directly visible. Too many lines may appear horizontally and vertically when there are a few containers on a screen and I wasn’t able to make distinction between these lines and where it will eventually place an element.
I just saw that in the API doc there is the “widths” property that may come handy from time to time and I didn’t see it in the properties dialog.
Anyway, I don’t use that feature too often. Mostly I use other containers.
George