Perkons fits on top.
About 5cm of clearance in the back and 7cm near the front, measuring to roughly the top of the support surface that the Perkons is resting on.
(FWIW, the Heli 2 is my favorite synth stand. It can hold anything from a Roland Boutique up to the Perkons and Syntrx. The angle is ideal (for me). Materials look and feel good, and it folds up nicely)