How to assemble a springform pan? The bottom sheet of a springform pan typically has bumps and a raised lip. Should the lip go up or down?

I've probably done it both ways in the past. Is it just a matter of personal preference?
It's personal preference.

However, it's easier to cover the base of the pan in grease-proof paper when the lip is downward.  When the lip is upwards, it can be difficult to get the lining paper into the edges at the bottom without it crinkling a lot.

You get slightly less mix into the pan, but it's not really noticeable.  For me, it's easier to handle a downward lip.