There are many settings related to the window size/position.
Do you the automatic workspace? Please check the Window tab of the Customize dialog. If you use the automatic workspace, then the last window size/position is remembered automatically.
If none of the workspace is used, then please check “Restore Tabbed Window Position” check box in the same dialog/tab. If this is checked, then the last used tabbed window position/size is used when the tab is enabled.
If none of these is used, after you resize the current window, you can go to the same dialog/tab, and click “Save Current Window Position” button, and check “Restore Window Position” and “Restore Window Size”, and the current window size/position is remembered.
I hope this helps. Thanks!