Reducing the power of power amplifier(changing drain voltage?)

hello amplifier experts,

Given condition:

I have a Power Amplifier that I designed for example 100W at 50V drain voltage. This will give me a first hand approximation of the Roptimum that i need to present to the amplifier output [Ropt=(Vdd-Vsat)^2/2Pout)]. Ropt=12.5 ohms

Now, I would like to reduce my power at 50W and 10W (assuming Vsat ~ 0). I would then compute the required Drain voltage for each of this power level assuming I retain the Ropt which is 12.5 ohms.

Question:

1. Since the amplifier is designed and matched at 100W with Ropt=12.5, will it still be properly matched at 50W and 10W operation when I lower the Drain voltage as computed using the formula above?

2. What can you say about the efficiency?

Thank you