Diopter for Hugyfot minidome?

I recently bought a Hugyfot housing for my XTi / 400D.

Does anyone have any experience with the Hugyfot mini dome port and the Canon 10-22mm lens? If so, do you know what diopter to use for correction?

Just to save someone else the trouble, here's the response I got from Hugyfot:

Dear Sir,

 

I am using a Canon 350D with the 10-22mm in the mini dome + 35mm

extension ring and a diopter is not required.

 

Vriendelijke groeten / Salutations distinguées / Kind regards,

 

Pascal Eeckhoudt

Marketing Green Force/Hugyfot

I'll probably order a set of diopters and do my own testing...