LOL! Actually, my answer given was provided by and based on your details regarding shifting weight while already on the scale (90 degree angle, vs straight up). With that the Dr's office scale would give the most reliable and accurate reading. There will be no learning on the wall at Dr's office, though I'm sure some have tried. Ha!
Obviously, not standing right on a scale will give mismeasurements, as I indicated in my above answer. I've stood on my toes before and that even distorted my weight. No matter it's about position control. Plus,, quality scales matters.
Thanks for your interesting question, and comment. The visual of both made me a smile.