Hubby made mine for my 7700...the needle is 11" back from the front edge. I find this comfortable for me with my elbows relaxed and slightly out from my body and resting near the edge of the table and my fingers near the needle to guide whatever I'm sewing. I am 5'6" tall and tend to have longer arms, I think, so these measurements might not suit a shorter person.
It also gives me a better line of vision as the 7700 has a somewhat bulky 'head' above the needle and I don't have to crane my neck to look under it to see the needle.