I will start compiling some notes, but I have noticed that I seem to be getting only really small science drops.
Usually when hero reaches levels 10, 20, 30 etc, you get the bigger size drops. My level 10+ hero was still getting the smallest drops, for 9 out of 10. Possibly less frequent too, like one fight out of 3 or 4 drop.
I have 6 fisher perk points equipped, which each give an extra 1% chance, of science find chance.
Chests are more like 99% smaller drops.