Roman,
I worked with Mohammed on this topic. He is the one that directed me in using facetStrain and facetStrainIncrement for different mechanisms, including thermal strains. He knows how the information needs to be passed to the material model and he did the debugging himself; he wrote the extended LDPM material model. I added the facetStrainIncrement arrays because he asked me to do that. I don't want to make changes since Mohammed is happy with the current status. You are welcome to talk to him and go over the logic. We chose to share the source files for the extended LDPM so that direct interaction between all collaborators is possible. Xinwei and I are not familiar with the extended LDPM material model. I am sure Mohammed will be glad to talk to you and explain why we implemented applied strains in the way we did.
Regards,
Daniele