I (mining at Amsterdam) noticed the same issue and yesterday H2O confirmed (on IRC) that currently not all servers give the same profits, but he is working on a fix. Excerpts from a chatlog (with other news as well):


Jan 31 22:23:03    Do we know why the difference in unexchanged between different MC users is so enormous? Are you screwed when mining EU/Amsterdam instead of US?
Jan 31 22:31:35    Acrobat: I know that's an issue. In the future, it won't matter what server you're on.
Jan 31 22:31:47    I'll make all shares equal
Jan 31 22:33:15    The difference in profit between the various servers should be smaller now, than it was before.
Jan 31 22:34:48    well, they should be. I made a change a couple of days ago that should make them more equal
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Jan 31 22:39:43    current plans, for those interested, are to fix the amsterdam server (I think I know why it disconnects a lot), then set up a new system for rolling out new servers.
Jan 31 22:40:11    So I will be able to easily provision new servers
Jan 31 22:40:38    Once that happens, we'll get a Dallas, LA, and Hong Kong server
Jan 31 22:41:03    both Ireland and Amsterdam suffer from the same problem. I don't know if either is best
Jan 31 22:42:28    I could do a Frankfurt server maybe.
Jan 31 22:44:48    Scandinavia will be low priority, because none of my hosting providers have datacenters there. I'd have to use a new one.
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Jan 31 22:46:27    Yeah, the current load issues are the main thing
Jan 31 22:46:33    Which I can solve
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Jan 31 22:47:27    I need to lower the diff again. But I can't yet.