I don't think you can do numerical.
Because they carry Images... Its like settings Officer to mean something other then what it actually means. It could but you would have to fight with your own understanding of it when reading.
The Index seems to work, but that is set based on meaning(strength of line), if we just add numbers without meaning I doubt it will work great.
As far as Images go, Si can show movies, spotlights etc.
And it seems in both cases the answer is Si.
(in first case as its the only moving line in second case it makes it simpler by just setting the Parent on it that you originally set).
I think the approach is very interesting and it could work, but with some slight adjustments.
One is to use Other line instead of Parent. Parent as communication/paper/knowledge etc. I get, but I think if a person(teacher etc.) is choosing the topic, there may be reason Si is on Officer, that is what is the choice of the teacher/system there. So safer to go with Other line.
The other is to use Images. Need some meaning to connect them. Fire lines as movies/entertainment may be wiser approach. Just my view, of course. : )