Hi Jesper - quite honestly, I don't know that I've ever noticed this, as if I publish dashboards with tabs, they generally tend to be all sized the same. However, I find the same behavior as you in my 9.2.0 environment. Is this a change from past behavior, or has this always been the case? It seems like it's in the realm of possibility that it's expected behavior if this is not new.
If this has changed from past functionality, I would file a case with the support team to see if you can get the official word from them, and get it on their radar if it is an unexpected change with your version.
I believe this has always been a problem with Tableau Server tabs going back to 8.X and earlier. If you publish with tabs, and any of the views are fixed size, all the views will be the max fixed size. The workaround if you want to maintain different sizes for your different views is not to display tabs.