Inkbrush supports fixed layouts for responsive design and uses lots of layered sections that can be switched off and on for mobile devices and desktops.
Conversely, Inkbrush doesn't support fluid layouts for responsive design, which use percentages to scale content. Inkbrush simply wasn't designed to support fluid layouts, and that's not the way it's intended to be used.
The core part of Inkbrush is chopping up an initial design. This means the email has a fixed size (or many fixed sizes if many images are used). So the obvious choice for us in adding responsiveness to Inkbrush was to use fixed layouts.
If you aren't using fixed layouts for your responsive design, we urge you to give this a try and see what you think. The fixed responsive system we currently have has been very successful with our big and small clients alike, and it does a great job of providing different designs on different devices.