I recognise the problem you are having.
I have found the best way to approach this is to add
DoCmd.Maximize
to the OnOpen event of all my reports, and also then to add
DoCmd.Restore
to the OnClose event of the reports.
This means that when the reports open, they will be maximised to the full Access window size, but after they are closed, my forms are restored to the normal window size. I find this preferable to including the maximise command in a command button - this works OK for opening, but unless you also include the code in the OnClose event, you will be left stuck with your forms maximised.