Totally agree with CW. Sadly, too many people don't even pay any attention to it, and for testosterone, it's (Free) where the rubber meets the road!
OP, you might see the variances as you noted, but do us a favor and take your Free Test and divide it by your Total Serum on any of your lab results (FT/TS = FT%). You should find that your actual percentage of Free Testosterone is fairly consistent. "x" percentage is the amount of actual bio available testosterone that is not bound by SHBG or albumin.