Sorry but it doesn’t sound like you’re really making any particular point other than being contradictory. From a UX perspective usability is far more important than “space priority”. If you can’t even read the labels on the tabs, as the design is right now, then they’re basically useless. Which is why this thread exists. Having them horizontal and able to flow over multiple lines, based on the width of the properties panel would negate this issue entirely. Agreed, that would incur a negligible cost in vertical space but this would very be minimal based on an average user having perhaps 10 or so tabs listed. Not to mention both this and the other option of a drop-down menu (which would be compacted in the header) would actually save screen space by removing the not fit for purpose vertical tabs.