How to derive peak pulse power rating of SS dual diode

Power transistors typically have thermal impedance graphs listed in
their data sheets. I'm not too sure how to use these graphs yet, but
supposedly you can determine the pulsed power limitations of the device
from it. Has to do in part with thermal mass of the part and heatup /
cool off times I'll bet. If anyone can lead me to a easy to understand
application note on the subject I'd be deeply appreciative.

Anyway, this information does not exist for small signal SOT-23 dual
diode packages. I've searched data sheets from 4 different
manufactures of devices like the BAV99 and BAT54. They just don't
offer this type of thing. I guess these devices weren't meant for
heavy duty operation so this data was not included. I'm not using them
to that capacity in my design. However, they will see the occasional
transient and I'd like to know if I am covered.

Will most devices have similar peak pulse power ratings given similar
physical size? I realize some have different electrical
characteristics but is that a contributing factor? or, is it merely
due to the thermal transfer capabilities of the package and size of the
die?

Thanks,

Ge0rge