Er, I think we are miscommunicating a bit here. I initially said that folks were probably gemming a lot initially due to the reinbursements and rewards this time around. I was trying to rationalize why I dropped in rank so rapidly the first couple of days (over the weekend). Since yesterday, I have reclaimed over 15k rank positions with now about ~9,500 of it occuring today in the span of 4 runs.
If the positions were based solely off of averages, then my rank would not change no matter how many times I would run it since I am not signifigantly improving my average each run (with two exceptions explained below). Furthermore I would be dropping in rank in any run that I did not score above my average in, which just isn't happening.
I have (later yesterday night) scored a medulla gem on the run immediately following earning a sacred jewel. I did nothing different. My units did not level up at all and I fought mostly the same units on each of the runs with only round 3&4 being different at all. It makes no sense, but whatever. If simply equipping 1 sphere on one unit is the difference of ~200k points (and a lot of rank positions for no reason), so be it. I have not since scored that high.
I am far more willing to bet that the very top end rank 1~3000 have such absurdly high scores totals (I'm gussing north of 50 million) that there will be little to no movement from here on out without signifigant gemming going on.
When I was talking about averages, what I meant is if you score higher on average then your total will be higher (average = total score / total runs). So I'm theorizing that nothing is weighted, you just get the score you get, it's added to your total, and then your total is compared against other people's totals. As one high rank data point, I'm rank 1885 right now, and my score is 4,929,634. I'm pretty sure this score is equal to the sum of all your runs divided by 10. I've run 59 times, so this would make my average 835,531. I'm not saying that the positions are based off of averages themselves, just that if you do score higher on average, then it takes much fewer runs to get a high score. The highest score on my friends list is 8,442,746, but I can't see what his global ranking is, only that score and the fact that's served 72 times (making his average 1,172,603)
I'm able to maintain this rank by running FH 6 times a day (3 in the morning, 3 before I go to bed), but that's all I'm doing right now. No gemming. But there's definitely movement. This morning I woke up and I was 2400. So I dropped by a fairly significant amount in just a few hours. But sub-500 yes there's going to be significant gemming.
About scoring, a very large proportion of your score comes from sparking. If you spark even just a
little bit better, it can definitely mean 200k points if you have many groups of 4+ enemies. The guy Ushi who does all the Youtube videos posted a video where he scored close to 1.2 million with Felneus + 5x Serin. I run Felneus x2, Serin x2, Cayena x2, with Lv. 10 BB across the board, and the most I can get is 1m and that's if I'm really lucky. The
only difference here is spark potential. 5 Serins will generate at least 20% more sparks than my setup, which definitely accounts for the score differential.
So in your case, the run where you got lucky, I'm inclined to believe all the stars lined up and you just sparked really well on every round. The fact that you jumped such a large number of ranks is because you scored probably 50% more than you usually score (and likely, what other people around your rank are scoring), combined with the fact that the score variance among users with similar ranks is much lower at those ranks, so an outlier in a single score will cause a larger movement.