It is good practice to ensure some design margin for the electronic circuit in terms of absolute maximum ratings.
What is the proper way of selecting such a margin for Total Power Dissipation?
Let's assume 20% as a safety margin for any reason and SOT363 NPN Transistor as an example:
On the chart below there is a common power derating curve for BC847 NPN Transistor in SOT363 Package - [Blue].
I calculated the -20% Power alternative [Green] it looks good however the closer we get to the Absolute Maximum Temperature Rating [150C] the smaller the margin becomes. This is why I wonder if it is a proper way of doing this?
As an alternative, I added another line which is basically -10C of the base the value [Green].
Is there a way to define something "in-between"?