Use the range in dashboard size.
set min and max size like
1020 and 625
2400 and 1320
I tried using the range in dashboard size, still it is showing the white space and is not aligned on the web server page.
Unfortunately this can be a number of things
If you have published in tab mode, have you checked your dashboards to ensure that they are all the same size ? Tableau 'reserves' the space for the biggest dashboard for each dashboard and this can generate a gap space (usually at the bottom).
Alternately, just making sure that you are publishing the dashboard and not the worksheet ? this can have some pretty random consequences as well inside iframes.
All the dashboards are of the same size and I published only the dashboards not the worksheets.I tried many times with different resolutions, still it is showing the white space on top and I should scroll down to view the entire dashboard.