Larry
Just another way of doing things, but I always put on my washes prior to flat coating; that way, if there is any sheen resulting from the wash, the flat covers it up. It's important to allow the paint to dry for a few days before doing this, but then I use more enamel washes than I do oil.
In addition, I spray Testor's flat right out of the spray can. Since it's a lacquer, it's usually fully dry in about an hour.
Also, one technique I find useful in applying flats: I'll often spray some flat out of the spray can and into a small plastic cup. I'll take a brush (round 1/0 or so) and use it to place flat in hard-to-reach locations (like gun cradles in artillery pieces, or suspension arms, leaf springs, etc. behind or near road wheels), so that I don't get any runs or thickened areas trying to force the spray into those areas.
If you have any concerns about results, check out the pics in my sig. They're in the Ron George gallery.
Hope this helps someone.
Gip Winecoff