Only 78 people in the whole of Catalonia have this surname. Unless some of them are reading this, we'll probably never know. I think you can pronounce it with /e/ or /ɛ/ whichever sounds better to you.
The provinces with more % of people surnamed Febas are Huesca and Lleida so Northwest Catalan would rule. However, I guess each one pronounce it with its local accent.