Hydronic baseboard

I am running hydronic baseboard from a room with a slab to a new room addition with an unheated crawl space. I need to loop the supply or return inside of the baseboard. Everything I read says loop the return line back over the fins. In my case, with the slab it would be easier to loop the supply over the element and avoid making a figure 8. Seems like a silly question but does it make a difference which line I loop inside?