Maybe this will help...

or the link below...

Looks like you want them between 6-8" apart, depending on how much projection off the rod you want when they're open and how much slouch you want when they're closed.

You may also want to look at ready mades to see how they're done or go to the fabric store and check out the grommet tape to see how they're spaced.

Here is a link that might be useful: Spacing grommets

thanks Anne, those do help me.

I have never done grommets before. A mock up sounds like a great plan.

I have a basic book for sewing window coverings and here is what it says about using grommets:

"Mark the placement for the grommets as for the rings, above." Use an even number of marks if the curtain will be run through by a steel cable or thin rod, so that both ends of the panel will turn inward."

Above they say to "place the ring end marks 3/4" from the sides." "Space the remaining marks every 6" - 10" apart. Try different spacing patterns, using safety pins to help you decide."

For the drapery panels in my home, I placed the ring clips 6-1/2" apart. The last clips (where the panels meet when closed) are about 1-1/2" from the ends. It provides enough of a little overlap for me.

This book also suggests to use an upper hem allowance two times the grommet length plus 2". So, your 4" upper hem sounds good. I wonder how hard it is to punch out/cut a hole through the fabric and the buckram?

Let us know how it's coming along and post pics if you can!

Laurie