Looking to Change Default Date Span

So, I have a question I can’t seem to find the answer to anywhere. What I’m looking to figure out is where the date range is defined for the “Evolution over the last (date/week/month)” graph.
The Day graph range seems to go about 1 month.
The Week graph range seems to go about 7 months.
The Year graph range seems to go about 10 years.

These seem to be a bit arbitrary, and with a new piwik installation, none of my tracked sites go back anywhere near that far, so I’d like to modify some of this.

I’ve poked around a few files, but don’t see anything obvious and i’m looking for help from some piwik experts.

So, the question(s) becomes, where are these settings held? Is there any reason not to change them? Any way to easily make them user/site specific?

Thanks in Advance!