Designing for DIN rail mounting - terminal positions?

Hi, I am designing a module which will be mounted in a DIN rail enclosure. The enclosure has options for terminals at the top and bottom of the unit. What are the conventions for terminal layout? I would like to position all the terminals either at the top bottom edge of the PCB, is this an issue? Which would be preferred? Is there a convention such as power in at the bottom and power out at the top, for example? What about the ordering of the terminals from left to right? I will be using barrier screw terminals with a pitch of 10mm, for 230VAC at 16A.

Any guidance or links to info in this area would be much appreciated. Many thanks.