ultra roadie

There is an expander inside the steerer, Canyon's own one.
I don't really understand how the headset cap I'm using (the one I've linked above, with a bolt and thread) would actually preload the bearings? Turning the bolt pushes a wedge horizontally not vertically so unless I'm not looking at it right it doesn't really do much.
The example pics I've shown above both use Canyon's expander inside the steerer (same style as I'm using) so I'm assuming it does preload the bearings similar to a standard expander and topcap.
It's hard to get an actual answer - here somone seems to agree 'Canyon ... use this locking type spacer so they can ship the bikes with the handle bars off without losing headset preload.'
And in a Canyon manual, I assume referring to the same part, 'Some models are fitted with a
transition plate. This part is designed to keep the set bearing play even with the stem or cockpit dismounted. This transition plate as well as the fork steerer clamping must be released to re-adjust the headset. The transition plate therefore only is an assembly aid.'

A round, very slim bearing cap would be fine. I think if it's very low profile it shouldn't look too out of place.