VR Converter shrinking final video size

I am trying to convert a fisheye video to equirectangular using VR Converter, but when I set my options it seems to half the size of the output? I am more familiar with premier pro, and when performing a similar operation using the EOS R5 VR plugin, the size of the output remains the same as the input, so I didn't think 50% of the scale should be lost during this operation - is there something simple I'm overlooking?

The Left fisheye lens video is 4122x4336 originally and after VR converter is exported at 4122x2056 (but with half of the 4122 as a black border - so in other words, essentially 2056x2056).

I can fake it back to the right level by scaling it by 200% but I'm presuming that will have lost some quality because it's still a 2056x2056 image that has just been scaled 200%?

If I remove VR converter it does take up the whole canvas:

I don't understand why it's adding a border and reducing the size 50%!

Thanks for any help!