The 1.3.5 update for MIDI Designer is out, with a lot of tweaks for scaling. It is a very pretty app, and now it should stay pretty no matter how much you resize and retweak the controls.
• Sliders, crossfaders and buttons are now aspect ratio independent.
• XY pads are lighter than ever. (WTF?!)
• Our signature knobs are sharper and more sizable.
The update notes also mention improved compatiblity with two-way MIDI hardware, when using the Pedal Board feature.
Here's a short demo of the new control scaling from the developer.