Your stick method is an interesting idea, but it doesn´t allow for a person to tell you how it feels during the process of opening and closing the bleeder, ie: mushy, solid, etc.

As far as missing fluid, I would check the lower front part of the booster where the master cylinder connects. It is possible to have fluid leak there without notice of it from above. During bleeding when the pedal is pushed to the very floor, fluid can escape the master cylinder and exit at that place. To avoid this, place a short 2X4 on the floor where the pedal would normally touch if pushed completely to the floor.

Of course you should check the MC fluid level after the bleeding of each wheel. It has to always be above minimums front and back chambers.

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