The number of player each group is stupid as of now

Group 1: 4-9
Group 2: 10-19
Group 3: >19

For 1vs1
When the number of player is 8 there's 3 match: 8, 4, 2, 1
When the number of player is 9 there's 4 match: 9, 5, 3, 2, 1
When the number of player is 10 there's also 4 match: 10, 5, 3, 2, 1
How come the group number is went up not when the number of player at 9 but 10?

Imagine you at a tourney with 8 player, oh there's 3 match only, the prize is right at group 1
Suddenly 1 more player join and the number of match went up to 4, but guess what?
The prize still on group 1
And one more person enter again so it's 10, oh the number of match does NOT went up again but guess what?
The prize went up to group 2...

The only thing the 10th player does is make one less person get byes but the number of match needed to win still the same, it does not make any sense if the prize went up at 10 instead of 9

The same problem occurs on 16 to 17 player
16 player means 4 match: 16, 8, 4, 2, 1
While 17 player means 5 match: 17, 9, 5, 3, 2, 1
But the prize went up when the number of player is 20 instead of 17

I propose the grouping changed as this:
Group 1: 4-8 (3 match)
Group 2: 9-16 (4 march)
Group 3: >17 (5 match and above)