From: http://thyrm.com/product/switchback-backup/ "...for SureFire Backup tactical momentary switch only; NOT compatible with clicking tail caps..." ; the Large doesn't have such a disclaimer http://thyrm.com/product/switchback-large/
Does anyone have an idea why that is the case? Best I can figure, the interior retaining lip might be sufficient to displace the back-cap into "storage\off" mode, but it's all hypothesis.
https://www.youtube.com/watch?v=sC90ZTLGnCQ (Thyrm for fullsize lights - shows compatibility with both momentary and clicky switches.)
https://www.youtube.com/watch?v=2QUtkFvItvY (Thyrm Backup for slimline lights - shown installed with a momentary\dual-mode light.)