Hi Robbe,
The top of the child MDI form when maximized will be rendered only below the RibbonControlAdv in the MDI parent form.
I have attached a sample that illustrates the same. Please have a look at it and let me know if I have understood your requirement correctly.
http://websamples.syncfusion.com/samples/Tools.Windows/F61974/Main.htmBest regards,
Golda