1.Maximum Settable Power is the maximum value that the API will let you configure. This value varies from module to module and is dependent on that particular module's components and what it could achieve during our factory calibration.
2. About the difference between Maximum Settable Power and Maximum Port Power, show as below :
Figure 2 is showing measured data on 1 unit as an example of what you get when you set your power to something above the "specification" range. So for example on IF0, the green line represents the highest values that particular module will let you set in the API, but the light blue is what the hardware actually achieves when you set those values.
Put another way, above the specification range, we give our best effort to hit the value that is set, but can't always achieve it. If you want guaranteed performance across all your modules, use values below/within the specification range.