Could use some help with this interface

[Mike Pliam]

I have been working with a MDI 3-way child splitter that works pretty well - but I cannot figure out how to precisely control the split windows.

The basic idea is to split each child window as shown below.

IOW, I want A and B to be split equally, and I want to be able to toggle (show/hide) C.

My problem is that in order to get the initial split that I want with each new child, I have used CChildFrm::OnSize to set up the split sizes such that every resize or new child or update reproduces the original split, making it impossible for the user to hide C as it keeps reappearing. While admittedly this is largely an aesthetic issue, it has bothered me for months, so I thought I would ask you all for help.

A sample demonstrating the problem is attached.

Thanks for any help you might provide.