Elf problem solved??
At a guess logging in every 4 hours (as compared to more frequently) means that the number of highly visible elves increases (and so you clear more) or a longer time away means that you have less elf ...
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If you only log in every 4 hours then you will be waiting longer to shoot your cannon which in turn will make you miss firing it a few times a day. That's where your extra elves are coming from.
