Thank you all for the clarifications, this helps a lot to better understand what is happening behind the curtain. Not being able to define an initial size of a WebSDK control is no big deal, only a nice-to-have. But for me not even important enough to raise a feature request 
But you can…in the Inspector Behavior dialog…
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Ops, my bad. Sorry, didn’t try now, as I understood Greg’s response as it would not work 
… Great day, all my “issues” solved! Again, thank you all!