Clear your mind and take a deep breath. The difference between the Highlight side and the shadow side would meter at 6.5 stops. In order to create this ratio the power of your lights woul be increased 3 stops. Keep in mind that each time it is increased a stop it doubles the units of light so (2x3=6) plus the overlap of the fill .5 = 6.5. This is why Michael keeps saying not to confuse exposure with ratio.
Ratios are not merely something we observe. We can create them. that is the whole point behind the math. To be able to predict and manipulate results.
There are a many reasons your tests may be yeilding different results. Distance of lights to subject, setting of power going to each light, bounce off walls acting like reflectors, use of any automated self adjusting devices on the lights. All of these things could be throwing your results off. Thats why they invented math. Trust the rules not your eyes. Keep running tests and making adjustments until you get the target.
Your rule of thumb was a stroke of genius and it works beautifully. Using your rule and Kirk's diagram I worked my way backward through the math. To get to know the rule forward and backwards.
As you can see we are all learning and re-learning on this thread, don't give up!