It is important to remember that the amount of light emitted from an Emitter is spread out across its surface.

This means that the same Emitter material will look dimmer on a large emitting surface and brighter on a smaller emitting surface. You may also think something is wrong when scaling up your small Emitter, since the amount of light falling on your subject looks like it has decreased:

The two emitters are using the same Emitter material. On the right, the Emitter emits the exact same amount of light as the smaller Emitter, but since it is emitting it over a much larger area, there is less light focused on the statue, so it appears darker.

If you would like to keep your Emitter the same brightness no matter the surface, then you should use the lumens/m2 units. Keep in mind though that this will actually change the amount of light emitted from the surface of the Emitter when you change the Emitter size.