Sorry for the late reply, guys. A lot of work and almost no time chatting... and all this with my ailing bones ..
I stumbled upon the cut and halve leaves technique as I tried to get more light into the lower areas.
I cut back the upper 2-4 pairs of leaves by ⅔ and noticed that all other shoots started to grow faster. Previously, I had often tied the upper leaves to a tulip with pipe cleaner so that the light could penetrate deeper into the canopy but this has much less influence on the growth of the side shoots. I believe that there are still many hormones in the tips of the upper leaves and that removing the tips has a similar effect as fim'ing but without damaging the meristem. When you fim' the tip but you cut a bit to far above the meristem you get the same effect as when you hit the meristem perfectly unless you still get only one main stem. But both plants would slow down in growth and are more focussed on branching for a while. I wont believe all the hormones evaporate just because the leaves gets bigger. They are only less concentrated and disappear as they get bigger and older. But in the very young leaves at the top are for sure enough hormones otherwise we would see not this behavior.
And if its still of interest, yes UVA will destroy insects dna and they can see and avoid UVA. A spider mite would hastily leave your garden or hide somewhere .. Nemadotes are for example dead within a few minutes "UVA radiotherapy", the harder the chitin armor the longer they can withstand UVA but they all don't like it and will leave your garden.
@Or_Gro
Halfing the leaves on cuttings slows down transpiration and helps to stop growing. In fact, rooting takes a little longer because they grow a bit further if you leave all the leaves on. You get yellow leaves cuz they have no roots and take nutrients out of the leaves just like when they get too much light. You can see new bright green growth within a week in this case.
If you have only a few leaves and halve a few of them additionally there are not enough nutrients left for new growth. But it's just enough to increase the "rooting pressure" to stay alive.(hope that makes sense).