OK, I got ya. I see nothing wrong with your multipliers then. There could be somewhat variation when taking and dropping the yeast slurry, but nothing over say 5-10% from calculated, if that much.
The bigger question is how to assess the density of the yeast slurry. If Mr. Malty suggests 150ml should be appropriate and, while you've got even more at 175ml, at the same time you actually count way fewer cells than Mr. Malty predicted, something is off.
It is an interesting experiment, indeed.
We don't stand alone in finding Mr. Malty quite conservative in both calculating viability and estimating needed yeast cells for a good and active fermentation. That doesn't mean it's wrong, those could well be optimum amounts, scientifically proven and all. At the same time, it doesn't negate the fact that with less than half you can still blow off your airlock, or fail to taste stressed yeast syndrome. People have done qualitative side by side comparisons with pitching rates. I'm not sure what the outcomes were, and they'd still be highly subjective by any standard.
The 2 injections of pure O2 surely helped in the growth phase, and those may have contributed more than a larger starter would have. The yeast coming out of the starter is used to 1.040 while the yeast grown in your fermentor has adapted to your 1.081 wort.