This is oversimplified statement. Damping factor is a ratio between load impedance and output impedance. Both are complex functions and frequency response is modulated according to this complex impedance divider. This is physics, electrical engineering and electrical circuits rule. No subjective opinion matters. I have shown numerous measurements here that show influence of output impedance to various speakers frequency response. I will not make a search job, I expect that any qualified reader understands.'damping factor' only matters at woofer frequencies and any number well above 10 is good enough.