I believe when you publish showing sheets as tabs that all dashboards share the size of the largest dashboard. The components don't change size, white space fills the gaps. If you publish without showing sheets as tabs the dashboards reflect the actual size in desktop.
Its tableau feature itself whatever the dashboard having highest size with that size only tableau dashboard will render in server
Hope tableau would take care in coming releases, meanwhile you can publish the dashboard by unchecking show sheets as tabs so that with same size it will render as it were in desktop
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