Mac mini screen real estate

I use my mac mini with my iMac, and with my Macbook Pro at different times. In both cases I use Screen Sharing to show the Mac Mini screen. On the Macbook Pro the arrangement is fine, but on the iMac I'm wanting to be able to see more real estate for the mac mini, and the window is pretty restricted. In Preferences>Display the only options available are 1280x1024 and 1024x768. Is there any way to give the Mac Mini window more real estate?

thank you!