Each of us are turned on by subjective factors - many of which we may not even be aware of - that influence how "attractive" we think someone is. And even that subjective evaluation is not static. It can change over short or longer times as we experience our lives. So what I may see as a "TER 9" right now may appear as an "8" an hour from now, only to come back as a "10" or a "6" the next day.  
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I don't use a hard value when I search for possibe matches. In the pro world, looking at only TER 9+'s will certianly mean I'll miss seeing some woman who might KMSO.  
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A well shot photo set, with good lighting and multiple angles will help me decide. But even then if the person who shows up doesn't match her pics, I'll probably end up "scoring" her lower (or perhaps higher) than my 1st impression.  
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Don't try to use some math equation for this. Let the small head start the process then use the remaining data (services, attitude, etc.) to refine your list.

I prefer petite slim women, but am quite turned off by fake boobs, the bigger they are, the quicker I give them a pass.  As an exercise I recently looked at the profiles of all TER Top Ten women.  Much to my surprise, I found only one who was all natural and also extremely attractive. The other nine?  I'd give them all a pass.  Yet these are top scoring ladies.  Just go with what your own preferences are, it's all you can do.