So that means that indeed, first player gets x*10 points, second x*7 etc. in the first step. Then player strength is calculated based on accumulated score/max score+max score/100 or something like that (you can do that many ways for similar results actually). Then you get a number between 0 and 1 as your strength, plus a decimal for the amount of games you played added to that (so someone who wins his first game can't be unbeatable). This number could then be the modifier used for the actual score.
So say your player strength is 0,7 and you win a game against 3 people with strengths 1, 0,8 and 0,6. This means you'll get a score of 4*10*1*0,8*0,6=19,2 from that game.
Of course, you only know this at the end of everything, because that's when player strengths are officially calculated. You can do preliminary calculations, but the scoring *is* dynamic.
Disclaimer: never did such a thing before.