Storyline Dimensions when importing into Rise

I have been searching for an accurate and solid response to the question I am about to ask. It appears there is no clear cut answer and so, I am hoping someone can provide a response.

Here goes, I am building a course in Rise. I am going to be using the Storyline Block to add further interactivity. I used 16:9 and turned off the player controls. However, when I import the Storyline file into the Storyline Block there is padding on either side of the file (see attachment).

So, I took a screenshot and made my next Storyline sample 1170 x 630 and deselected each of the player controls until there was nothing that could be visible in the way of controls. I then had another look (using a different color sample) and it appears a frame was placed around the file.

The options it appears to be, turn off the player controls and use 16:9 and see the padding, or deselect the controls individually and have a frame around the Storyline Block.

Which leads me to my question, what is the optimal (best size) to create your Storyline 360 file if you are planning on using it as a Storyline Block within Rise. 

Please refrain from simply saying 4:3 or 16:9 because I have attempted this and the frames/padding appears in both instances.

I would really just like to know a definitive size like 1000PX x 700PX or something like that. A dimension that has been tested by the Articulate team and one that works well. 

I appreciate any and all assistance with this one.