Acoustic Guitar Construction

In the midst of my first scratchbuilt project - - - ran into what is, to me, an ambiguous situation:

Is the upper transverse brace (the one behind the soundhole with the hole in it for a truss rod wrench) flat or radiused? I'm following Ken's instructions, but his are kit instructions where all the bracing is contoured as needed out of the box, so the question never came up. The brace sits roughly at the point where the sides are trimmed for the neck angle, so I can see the brace being flat, but I'd love to have some reasoning behind my SWAG.

Thanks!

I use a flat brace. The radius imo is mainly for the lower bout.

I flatten the center of a transverse brace radiused to 40'. Basically flat but I think it has a better transition close to the rims. Not sure it is worth the effort.

I go with flat.

Flat.

Similar to John - mine are flat in the center 2/3-3/4 of the length, with a very slight fall off out at either end to transition into the 40' radius I sand into my top rim..

Functionally, I'd call it flat.

Thanks, folks. Flat it is.