Do Hype Scene attributes dictate full screen presentation of an iBook widget?

I am relatively familiar with Hype and it’s use to create widgets in iBooks. I have a good few examples working - but am struggling to understand the parameter(s) that trigger a consistent full screen presentation of widgets from within an Ibook across multiple iPad device types.

I have read and downloaded a lot of material from this excellent forum - and understand (and have working) the following:

The recommended use of 1024x768 as a landscape scene size
The automatic generation of standard and @x2 assets from images that are placed within the resource pool - I am using 4096 and 2048 wide as per Apple guidelines
The difference between on page and full screen radio buttons within iBooks author

Where I am struggling is with scene size which seems to be critical in allowing a full screen presentation on the iPad Pro

Using a Hype scene size of 1024x768 (and the auto breakpoint width this provides) - I get full screen widgets within an iBook including the above images on an iPad Air 2, but reduced size on an iPad Pro 1st gen (similar size to the iPad Air 2 screen in fact comparing the images side by side)

By experimentation and looking at another problem, I discovered that if I change the scene size to 1366x1024 - full screen widgets appear on both models of iPad - whilst making no changes to the images already within the Hype project. This Scene size is fine in principle, as images auto resize to fit this scene (well enough anyway) - but why is it working this way - and will it present a problem on older devices for example?

In further experiments (which I have now run out of time to continue!) incrementing up the minimal amount to maintain the 4:3 aspect ratio from 1024 still produces the smaller Pad Pro image, whilst incrementing down from 1366 maintains it. I have also opened up the widget file and looked at the assets Hype is producing - and there are indeed standard and x2 assets in there.

Is anyone familiar enough with this behaviour to explain what is happening please? According to all forum articles I have read, the use of scene size 1024 should be sufficient to allow presentation of the large image asset - and I am assuming this would be full screen.

Thanks in anticipation - I look forward to the ‘doh!’ moment!

In iBooks, with a Tumult Hype Widget, Full Screen mode is... meh... not full screen like Flash works. Once the Hype project reaches it's full size, it stops scaling. That's why the larger 1366x1024 works. The project will scale down on a 1024x768 screen – but a 1024x768 project won't scale up to the 1366x1024 screen.