Hi Hemant,
You need to use a DockingClientPanel if there is any controls which are not docked.Place that controls inside the panel.It will take care of the spacing when user opens a hidden window for giving input.
I have created a sample from your description and attached here.Please look into that and let me know ,if you have any queries
Thanks for using Syncfusion Products
Regards
Joy
sample_fr41204.zip