Experiences with dual EDF's based on thrust angles to determine.
1. EDF transport when trimmed and flown level, if you change thrust and the plane climbs or dives, then you need to add up or down angle to the mount. You also should try this in a vertical axis. I ended up increasing the wing angle by 1 1/2 degrees to fly level when I changed power..
2. In order for my SR-71 to fly good, had yaw problems with motor setup. Since no two motor/esc/EDF's fan are the same(set up used 1 battery source) I had a crappy pair, so changed motor which solved yaw problem.
3. Designed and built my own A-10 and using 2 thrust vectoring nozzle that change exhaust nozzle angles so I could get it to fly level and straight when changing thrust.
What you should do is when your ready to fly yours, do a static test. Go in a closed area, hold your plane vertical, add throttle until it begins to hover, do a real quick, release grab and see it it tends to yaw, pitch quickly. If it doesn't go out and try it.
I designed and built an EDF trainer with one 64mm EDF mounted above and ended with 3 degrees up and one degree towards the right to make it fly real good.
So to answer your question, maybe.
Are you putting rudder or differential thrust for yaw conditions?