I think the reason behind this is that in Codeforces, if two competitors with a rating difference of $$$400$$$ compete in a single contest, it is expected that one competitor is $$$10$$$ time more likely to win the contest; and with a rating difference of $$$800$$$, the ratio becomes $$$100$$$; with a rating difference of $$$1200$$$, the ratio becomes $$$1000$$$, and so on...... (it's actually not bad to think that the ratio between any master to tourist is no more than $$$13183$$$ LOL), but in Atcoder the $$$400$$$ becomes $$$600$$$, so lower-rated participants in Codeforces becomes even more lower-rated in Atcoder, while higher-rated participants in Codeforces becomes even more higher-rated in Atcoder......(the bound between is extremely high, namely $$$3169$$$ QWQ); additionally, I personally think that Atcoder choses a rating calculation method more optimistic and tends to give more importance into "good times" contests of a participant, while Codeforces is more pessimistic and and tends to give more importance into "bad times" contests of a participant. Maybe there's consideration behind this ^_^.

Yeah, the same blog.

cool story