u could just use straight up paperclay but as u saw they created a barrier between the apoxy w clay so u should b ok. i personally would do a base of model magic then covered w paper clay then sanded then another light layer of paper clay to give it the smoothness.
Adelheid (KHR!)- 85% done
Fem!Austrian War Succesion France (Hetalia/Nyotalia)- 10% done
Fem!Izaya (Drrr!)- 90% done
Magent!Teto (Vocaloid)- 95% done