5:43 AM, Monday August 16th 2021
I am not nearly as far as you so I won't answer in regards to any official DrawaBox way. I will just answer for the other 50% of drawing for fun.
I suspect that you would be better off simplifying the forms to the point where the intersecting feathers are mostly just texture - with only a slight consideration to how the feathers would impact the outer contour of the wings. Rather than trying to wrap your head around all the layers of feathers and how they interact.
Here is a video from John Muir Laws on youtube that might help with drawing bird wings. https://www.youtube.com/watch?v=aGzpRSN1X3A
He has a bunch of other videos on a lot of animals. And more on birds.
There is also Aaron Blaise. I know he has a huge series of videos on drawing specific birds but I am not sure how much of it is free on his youtube channel.
I hope that helps.