@marktheshark of the sound is listenable the amp may be running hotter than optimal and producing more distortion. The volume attained and dynamics will level out. It’s like running a car engine. It’s always best to not make the engine work harder than it is designed to do for best results and longest life.
With flea power amps you will get the best results with speakers that are easy loads to drive in terms of impedance. The if they are also efficient they can go louder and clear as well.
I have looked at Fortes. Personally I would not chose them for a SET and expect best possible sound quality.
If you do not have to go very loud, I would recommend investigating Fritz speakers . These are generally designed to have benign impedance curves but are also monitors and efficiency is very modest. I have heard these at shows with flea power tube amps and was astounded with the results in a modest size room at least. Larger rooms are always a greater challenge but even in case adding a powered sub or two along with an active crossover to limit bass extension in the mains can address that