Blender fbx to unity weight painting problem

What's going on? Please help.
This is a bird wing. It moves fine in Blender, but in unity the weights are all or nothing
I'm fine with skinning arms and legs.
Is it because the bones are outside the mesh?

Here's the blend file:
https://www.dropbox.com/s/fia2w02bdksrgk1/BoneTest.blend?dl=0
Blender 2.79
Unity 2019.2.0f1

 

Solved - In Unity Edit - Project Settings - Quality - Other - Skin Weights = 2

 

Thank you so much, I had the same issue in Unity 2020

 

you saved us a big headache, thank you!

 

Godsent!!!

 

it doesn't fix the problem in my case

 

This solved my problem by adding skin weights = 4 in my case. Thanks so much for this @The_Mean_Fiddler!

 

Fu ck and i was like why it is working in blender and not in unity i destroyed my 3 hours

 

You are an angel. Thank you so much.

 

Jack Black bles you!!!