This info is probably here somewhere but for the life of me I can't find it.

Some forges have the burner directly above the metal.  Some have them directly to the side of the metal.  Others have them at around 20-30 degrees off center on the top.  Why?  Does it really matter?

It can make a difference but a lot is personal preference. The flame heats the forge liner and the hot liner transfers the heat to the work via IR. Aiming the flame directly at a wall causes a hot spot there with the rest of the forge cooler. Work in the forge can cause a heat shadow again making heat uneven. Not a big deal really but it can make a difference if you're heat treating finicky things say knives.

Aiming the burners to make a vortex circulates the heat more evenly in the chamber for a more even chamber temp.

You need to experiment and find what you like best but if you let the chamber come to a good heat the flame direction doesn't make so much difference, it's just keeping everything hot.

Frosty The Lucky.

I have a circulating flame set up and like it very much as I still have a hotter side and a cooler side and can place work to my advantage in it---eg recently we were heating some 1" sq stock and some 1/4" sq stock. Turned up the propane and put the 1" stock in the hot spot and was able to heat 1/4" to working temp without it melting...(yes I have melted steel in my propane forge; which makes me wonder when folks tell me propane forges don't get as hot as coal forges...)

I have used a few different gas forges ( including those of a well known knife maker ) each with the burner angled to supposedly get the circulating flame, however it just creates a hot spot on one side of the forge and cooler spots elsewhere. I guess that can be useful?  Although I tended to find it annoying with multiple bits of metal in there at one time

I just built a gas forge an have the burner vertical as I figured That I'd rather heat the metal than just the side of the forge. But like Frosty said you need to experiment to see what you like.

Gees, thought I had more posts here than that... Sure of it, been a member since 2011.

And then, we have flames from ribbon burners, which completely change the ol ball game; I like that