I am glad the suggestion worked. Rest assured I am still struggling around in the foothills of MC after several years - but it's worth it. Learning Mac basics and MC at the same time is adventurous. The program is of amazing power and flexibility in file handling and display. The biggest challenge is the lack of a coherent and up to date manual but the MC Wiki and this support board go a long way in filling the gap. Brian is one of several support experts, gifted with enormous knowledge and patience, who do a great job in responding.
It helps if you can supply basic details of your mac hardware and operating system, plus the version of MC that you are using when seeking advice. The Mac data is to be found by clicking on the white apple at the top left of the screen.
To your problem, when you have the RM&C screen that you have showed, can you not then drag the lower right hand corner to size the box to your preferred size? If you click on green after that, my box toggles between the reduced screen and the full screen that you show. You should be able to restore the box to a more reasonable size. The text size is altered by choosing a size under the 'View/Size' MC menu along the top but this also alters the text size in the main display as well. Text can also be altered under Tools/Options/Tree and View - select font.
Good luck in your mission.
Finally, for Brian, I notice that if I click on F6 more than once, I bring up a new RM&C screen each time. Is this deliberate? I would expect it to toggle the RM&C screen on and off? Its not critical but unusual.