Cognos Analytics

We have a requirement to create a Cognos dashboard having multiple tabs, let's say Tab1, Tab2 and Tab3. Tab1 and Tab2 are having 4-5 visualizations which is easy to accommodate but Tab3 has 7 viz which requires increasing the height of this tab page. When we do so(by changing the Preset property of Page Size, say "Legal" here), it affects all the tabs and the viz in Tab1 and Tab2 are automatically expanded to fit which makes them significantly bigger as compared yo viz in Tab3. Even if we resize these viz there is white space left.
Has anyone experienced such issue with dashboards? If yes, please let me know if there is a solution.
All suggestions are appreciated. Have attached sample screenshots of Tab1, Tab2 and Tab3 each with Page size "Screen 16:9" and "Legal"

There is no way that you can have different page sizes for the different tabs. Which means that every tab will have to be the same size as the biggest tab you need.

However, have you tried changing your dashboard from relative to absolute positioning? (Property of the Dashboard Canvas / Layout Positioning)  

This will then allow you to set sizes in pixels rather than percentages.

Whilst you will still end up with long pages, you will be able to specify visual sized in pixles, meaning they will only take up the part of the canvas.

You could create 3 separate dashboards, each with their individual canvas sizes. Then use the link widget to create a navigation menu between these dashboards so it appears to the user that you are within 1 dashboard with different pages sizes. If you also hide tabs in preview on all of these then it works pretty well. The only downside is that you will have multiple dashboards open in the switcher menu unless you can find a way of closing them on click. Hope that helps, not perfect I know but it does what it says on the tin.