Is it because your glass bottles are smaller than they should be, or does TFA put e than 4oz of flavoring in the bottle? I only measure what I take out, never measure/calculate how much the bottle actually had in it.
I had posted about this a little while back. The last bunch of 4oz bottles I bought actually had a spec sheet with a CAD diagram showing dimensions and tolerances, etc. Their regular fill capacity was something like 118.2 or 118.4ml, with an overfill capacity of more, something like 122ml or something. I have generally been filling these bottles up past the "stop ring" for the cap -- basically as much as I can get in them and still get the cap on tight without displacing any volume with the poly cone insert (which sticks down a bit) -- so I am pretty sure TFA is just filling their bottles a little over to make sure they're providing you at least 4oz.