How do I use MaximumWindowExtent to set a view's dimensions?

Question

When I create a View, I would like to specify a square that scales well to different displays.

In the dialog that defines the view, I am presented with a default Box that specifies dimensions as percentages of the width and height, based on, presumably either MaximumWindowExtent or MinimumWindowExtent.

However, I want to base the width off of the height.  Something like:

0.02@0.02 corner: (MaximumWindowExtent: y*0.75)@(MaximumWindowExtent: y*0.75)

If I cannot initialize it at creation time, what's the syntax to change it onEntry in the InitialState?

Comments

Trial and error is getting me partially there, though it seems ugly. After defining a view called "Box", I added the following to onEntry in InitialState:

Box corner: (MaximumWindowExtent y asFloat / MaximumWindowExtent x asFloat) @ (MaximumWindowExtent y asFloat / MaximumWindowExtent y asFloat).

(I used the "y / y" portion because I don't think I'll be staying with 1 as the height and it will be easier to remember and modify if I keep the ratios in my head.)

Debug := true shows me that I'm getting the approximate values that I want. I think.

However, I don't know what to add after that to force it to redisplay the new size.