FTP Different on Hills Vs Flats - Should I Adjust My Trainer Setup

I have discovered that my hill climb FTP is about 7% higher than my flat land FTP. Research indicates it is due to engagement of more muscles during hill climbs. So my question is should I set my trainer up so my bike is on an incline so I am replicating a hill climb with my body position and getting more muscle engagement or should I keep my bike level to focus work on the isolated muscle group?

My events are endurance 200+ Km between 2000M and 5500M elevation gain