Hmm... this worried me. I hadn't accounted for the different drop sizes because I converted my Miracle-Mineral-Supplement to eye droppers so that I get consistency with whatever solution I mix up - since I place them all in eye droppers.
I ran the comparison 3 times and I come up with an 87% ratio.
In other words, a standard eye dropper appears to measure out to 87% total volume with 40 drops against the plastic bottles. In my case anyway, and I have the very standardized 2oz brown glass dropper bottles.
Bummer...that means when I thought I was doing 15 drops, I was really only at 13 drops, and at 10 drops I was really at 8.7 drops. Oh well - it's very close, but this would be something to consider for anyone using eye droppers.