Just to give you some reference, I have a bridge hammock that started out at 54" raw fabric width at both ends. I have a 36" spreader bar length between notches, and a 30" suspension triangle side length. I am a portly fellow and used 1" hardwood dowels sold at Home Depot. My local one has them in 48" length at I cut them to 37" and cut 1/2" deep notches to fit into the corner rings I use.
The closer the ratio of spreader bar length to fabric width at either end approaches 1:1 then the longer the suspension triangle length you will need to minimize compression forces on the spreader bar.