I have noticed that older movies which have black bars along the sizes (to give a square picture. Like 4:3 ratio) don't show any lights at all for the sides.
On your website autofill black bars is an advertised feature. It would be disappointing to discover if it was for top and bottom black bars only and not the sides too.
There are a lot of older movies and TV shows that are 4:3.
Even the example in the video below from rocky horror has very thin black bars on the sides and it still gives 0 light feedback.