> Aaand, here you go:

So far I'm pretty sure that we have some rounding problem here - maybe
due to scaling.  The last version of my patch is attached, please use
that for further experiments.

Now first do what you have done so far (three iterations) and post the
results.

Next, if possible, try to turn scaling off, do the same experiments and
post the results.

Finally, with scaling turned on again, start Emacs with

--eval "(setq frame-resize-pixelwise t)"

do the same experiments and post the results.

Thanks, martin