Sandbagger, I'm not sure what you mean. Are there different shaders for each aircraft, that's why I'm getting different glossiness levels with the same Workshops settings?
Just a guess - I could be wrong.
It could be the way the different aircraft skins were created by the skinners. Each has his own software preference and techniques, so maybe the various aircraft types react differently with the game shaders.
In the earlier aircraft skins, some has 'lighting' added to replicate what the shaders now do. Could be it's those types of skins that vary to other later skins that don't have this 'lighting' added.
You can see this 'lighting' if you scan through the skins using IfanView. Check the Strutters (as that's the one in your shot) and you can see the 'lighting' texture on the side of the engine cowl.
Does a particular aircraft type vary to another type with the same settings?
Like I say it's a guess and could be a red herring.