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One variant @ 640px & Main at 1280px.
Scale to Fit Width upper to 1920px.

Clearly, you have to experiment.

Acorn

Sorry I did the same but failed to mention it.

Acorn

Marc, the page works both from the Xara file and your web page for me.

Perhaps clear your browser cache (Ctrl+F5).

Acorn

They do not show and probably for a number of the reasons I listed.
If I switch to Desktop Mode on my phone, things appear.

There are simply too many things going on that could confound the...

I can't help with iPhone, sorry.

Two Variants is overkill - use Scale to Fit Width and a single 640px Mobile size.
I would avoid the use of the HighSlide carousel as you are duplicating images...