Hello, Michael (@AMDGIHS2019),
I can definitely say that:
The TOP-100 accounts for about 3.7% of all postcrossing postcard registrations.
The TOP-1000 ~ 21% of all registrations.
The TOP-2250 ~ 31% of all registrations.
The TOP-5000 ~ 43% of all registrations.
The TOP-10000 ~ 54% of all registrations.
…
The total number of active accounts has not changed in two years and is approximately 800,000 members.
The organizers delete inactive accounts, so there are about the same number of arrivals as they are deleted.
That is, the proportion of really active players is extremely small.
I think @paulo and @meiadeleite can confirm this 