Portraits - Random?

I post this in the hope that those who read it won't consider it perhaps one of the most vapid matters ever to hit the modding General forum. And, yes, I am genuinely interested in replies!

Factions draw on their cultural portrait pools. Each faction (from the same culture) seems to have a different portrait set as their hard-coded default portrait. The second tends to be the same too, as he is often around at the beginning of the game as heir.

The brief tests I have done seems to suggest that

(a) factions of the same culture do use the same protraits at times
(b) there seem to be sequences of numbers that re-occur

After a little more testing I do not think certain patterns exist just within a certain faction but are true of the whole culture.

This leads me to conclude that there is no way of setting the portraits up (in their numbered files) so that one can have, mostly at least, some degree of control over which faction receives which portrait.

Has anyone discovered anything different? Has anyone even bothered to look into so mundane a corner of the hard-coding? Probably not :)