Cull/Create Inequality to adjust Surface Domain

Hello, 

I am attempting to set a limit on how small the surface division can go. The attached definition is working well, but creating divisions that are too small to be usable. I wish to cap how small the domain goes with an inequality or more suitable method. 

Any ideas would be greatly appreciated. All data is internalized. 

Thank you. Snipping%20GH.PNGGH%202.PNG