I was able to work out the measurements and the alterations I wanted to make on my existing bag pattern last night. This morning (using my 2 hour 15 minute pre-school time) I made this prototype.
I am very pleased! Normally in my first attempt at an alteration in a pattern I bungle the measurements. I under or over estimate my actual seam allowance. But this turned out as I envisioned it. In future bags, I think I might make the flap longer. Of course I am still struggling with the closure issue. (Who doesn't struggle with closure issues, right?) None of my totes have closures. I purchased a few magnetic ones, but I haven't tried them out yet.
You can see the lining of the bag in the last photo. The black with maple leaves is the pocket.
Any thoughts?