The indicator scaling only works when you tell the viewer its "base width", i.e reponsiveBaseWidth property that you would see in the published html if you publish a project using the Responsive template on the Publish form in SpotEditor for example.
In PixRiot previews you mentioned, reponsiveBaseWidth property can't be used as the previews (or iFrame embeds) there are auto-scaled via parent html to fit the browser window (100% width and height), i.e the viewer doesn't have to scale itself, which this property would force it to otherwise.
To support your use-case (which is similar to the "Mobile full-page iFrame" template on the Publish form), we now allow passing responsiveBaseWidth in the xml in the <control> element.
It's automatically inserted there in the xml config, if you publish a project using the Mobile full-page template in SpotEditor starting with late v3.6.5 betas and now v4.
Code:
<control dragSpeed="0.13" doubleClickZooms="true" disableMouseControl="false" showHighresOnFullScreen="true" ... centerZoom="false" maxZoom="100" responsiveBaseWidth="600"/>
So you can either re-publish your project again by making sure you select the "Mobile full-page template" and re-upload to PixRiot, or add it manually in the published xml as per the example above.
The responsiveBaseWidth in the xml will not force the viewer to scale itself. Instead it will be used to scale any hotspot popup images as well as indicators. It's the width at which a hotspot indicator is showing at 100%. If the view is sized smaller than the width, the indicators will scale relative to the amount of change and will stop at the minimum as per your screenshot below.