Getting a good acoustic environment in a small room is generally hard to achieve as there is little available space for acoustic panels. Home music practice rooms are a good example.
Often these small spaces receive little to no treatment at all.
One way to provide for a good setup is to have one end fully absorptive with the other diffusive. This allows more varied responses for different instruments.
Diffusers, especially on the ceiling, can give a sense of a larger space.
To ‘replicate’ a similar sound to playing onstage the absorption wants to be ideally 50-100mm thick.