While trying to place Astra smokes almost pixel perfect I noticed that they tend to lean toward the way you're facing while in Astral Form.

Make sure to face the correct direction when placing stars!

Apparently while in Astral Form you want to be facing the direction you want the smoke to cover properly otherwise there could be gaps in your smoke so be careful.

Edit: The smokes BLOOM based on the direction you are facing when you PLACE them.