Oh, I see what you're getting at. Yes, strictly speaking, that's true. Whist we're at it, we might as well use 63A MCBs for all fixed loads unlikely to create an overload (showers, immersions, conventional ovens/cookers etc.) - provided only that Zs was low enough for fault protectionNo, it only has to be greater than 33.9A - which you said it was - the shower cannot overload the cable.
Kind Regards, John.