DMF and eye-start AF - kind of 'continuous'?

On A-99, I've set to DMF with peaking on, and have the viewfinder 'eye-start autofocus' set on as well.  Seems to me like it almost continually AF's as I move a bit, vs. what I thought it would do (AF once then let me manually fine tune).

I know, "RTFM", and I will, but just thought I'd push this out there in the meantime.  Is that expected behavior?  Or am I just bobbing my head off and on the eyecup (I do wear glasses vs. adjusting the viewfinder diopter, so maybe I'm at a detect threshhold on the eyestart?)

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budding (translation: currently incompetent) underwater photographer wannabe http://www.flickr.com/photos/rtrski