Print borderless with InDesign and Epson P706

Some printer (drivers) might do that, but my experience is that borderless==photo printing and for stock of standard photo sizes, printing was 1:1.

It may be that this printer and others like it only do borderless up to, say, 8x10, and does not allow it on larger sheets. 

When working with this printer it's important to understand whether your content is being scaled up for borderless printing, or scaled down for standard printing with a border.

While Robert's suggestion for doing a test print with numbers at the edge is one good method off determining this (and I used to print a test sheet with precisely scaled numbers -- essentially mini rulers -- extending out both ways from the center on the x/y axes near the edges to see not only scaling but positional drift off center) you should be able to tell from your two prints you posted by comparing the distance of the star or rabbit ears to the edge of the print area with the measured distance to the edge of the page in InDesign (the Measure Tool is grouped with the Eyedropper).