My guess is Arne is going to be really busy with all the contract stuff, so if it helps, what I've learned over the years
- ARB is pegged to recent free agent spending. So, if Patrick Corbin went for $29/3 in one league but $13/3 in another, that affects what Kyle Hendricks will ask for this year (generally, he'll ask lower in the league that spent lower). This applies to all positions, which I think creates a bit more variance for position players where there are fewer comparable ARB cases
- All positions have caps for that service year (though these are league-dependent). I've inquired about this before and Arne says it's to avoid "runaway" salaries. The simplest example of this in action, in my opinion, is that you'll see Kyle Hendricks and Jacob deGrom historically ask for the *exact* same ARB figure in most leagues (actually, all of them I'm in, at least in 2018 and 2019), even though I think it's fair to say the latter has been a considerably better pitcher (including by RAP) than the former.
The simple answer to your question is that the algorithm is league specific, i.e., it looks only at the prices in that league and not across all of Mendoza. Some leagues have higher payrolls across the board than other leagues, which is reflected in the arbitration numbers.