Then based on this, it appears that I was on the very, very extreme end of preset insanity. Any combination of 2 presets that I do helps decrease the RMSE.
Ergo, I have artificially inflated my RMSE.
I am now more eager than ever to know the actual threshold of cards in a deck that deserves a preset so that it doesn’t artificially inflate RMSE (Something like a preset for every 1000 cards, or a 20 presets for 10000 cards or something), even more so for a mechanism that does it automatically.
In my case, calculating for different preset combinations is too time-consuming. I think I will stick with a preset per subject basis, though this may be on the other extreme end (too few presets per cards).
There has to be a sweet spot between number of presets and total number of cards without it damaging the RMSE.
My main concern about presets is that they often overlook appropriate intervals for very difficult (outlier) cards, so they are having a very hard time to schedule appropriate intervals for them, hence my behaviour of setting a preset for every single deck.