Blending two normal maps on Separate UV channels

Good evening.

I am trying to blend a Normal Map Trim texture that is on a different UV channel (Channel 2) using DeriveTangentBasis. My main tiling normal map is on Channel 0 and Light maps are using channel 1.

I was following the info here using the new Derive Tangent Basis Node for my Trim normal map on Channel 2.
https://forums.unrealengine.com/showthread.php?45063-Multiple-Normal-Maps-on-Separate-UV-Channels

I have unchecked Tangent space normal map in the Material and converted the normal map from Channel 0 using TransformVector - Tangent Space > World Space.

In Picture 1 it appears to be blending as expected, using the material setup from Picture 2. However when I try to blend using Material Functions I am getting poor results. Picture 3 shows my material using material functions and Picture 4 shows that result. Does the math need to change when using material functions?

If someone could take a look and provide feedback, that would be great!

Thank you.

Chris.