Welcome to the Hailo Community!
Please have a look at the following post:
Hailo Community - My model runs slower than expected
Power is to a large part linear to work done plus a bit of static power. So, when you run the model at half the FPS you will measure half the power.
When you use non-blocking code (not waiting for the result) FPS is not the inverse of the latency. The Hailo-8 can process images in a true pipeline. As soon as the first layer finishes one image it can start processing the next while the other layers continue processing the previous frame.