Maybe try actively pulling your arms down and pulling your lats back. That will make it easier to start more upright since your effectively elongating your arms.
Also, start with bar around midfoot if you aren't already and start with your shins against the bar and imagine keeping rigid shins and pushing your pelvis forward. This will help keep you in a more upright position as you break the floor and first part of the lift.
Since it's just a frame, I can't tell if you do it or not, but pull the slack out of the bar. If you hear a clank when the barbell hits against the plates, that's a sure fire sign you're not doing it.
To pull the slack out, you start with your lats pulled down and back. Grasp the bar, then almost kind of lean back some and apply a little bit of pressure on the bar so that the bar is already against the plates. When you put bigger poundages on the bar, it'll even bend. Then you try to push your feet through the ground full force while keeping everything in your back super tight.
Not doing that often leads to the weight getting in front and/or a rounded back. It's damned near impossible to keep the back as tight as you need to without pulling the slack out.