Horizontal wave patterns on bottom of print

[mattiasr]

I found someone with a similar problem here:

Horizontal undulation (wave line)

Hello, finally I got form1 and I’ve just printed iPhone5 cover with it. Simply one question, please refer to the photo.  There are many and deep horizontal wave lines on the side, however there are much less lines on the case top side (left part of the photo), and on case’s back, it is smooth like mirror surface !! Those surfeces are the same thickness, and so I think it is not caused by too-thin model design. Does this difference come from surface’s angle or machine’s "directional charac…

But no info on it being solved or not.