ADAPT_TAPERED - when is the day half over?

The description for ADAPT_TAPERED has remained pretty consistent in the documentation and help text for as long as I can remember - basically: "ADAPT_TAPERED allows for running over the dropped percentage in the first half of the shift -as defined by call_time selected for campaign- and gets more strict as the shift goes on."
What determines the start time of the campaign? OR - what determines when the campaign's day is half over - or the time that ADAPT_TAPERED begins being more strict about the max drop rate?
The reason I ask is - given consistent values for Average Agents Logged In, Max Dial Rate, Max Drop Rate, Actual Drop Rate, Local Call Times, and Latest Server Time - I have been noticing that some days, when we've over the max drop rate during the first half of the day (which is EVERY DAY
) the dial level ADAPT_TAPERED uses seems to drop earlier, more often, and more dramatically than other days - which makes me think that the "first half" of the shift is over earlier on some days vs others. I wouldn't care - except that some days, it gets pinned at "1" - and our agent wait time will climb into the DARK-DARK blue - several minutes. Usually - once it goes into the DARK blue - it starts growing again automatically - reps/ managers don't like waiting 1 minute - they're used to under 20 seconds - but - as long as it's responsive and recovers - it's usually "ok" for the most part.
This system is (still) running SVN 2973, Vicidial v2.14-670a, BUILD: 180424-1521, DB Schema 1542 - so - if the rules have changed for this in later versions - I would be very appreciative if how is included in anyone's answer.
SO...if I knew what caused the system to think that the first half of the shift began - I might be able to control this a little better and make this too, more consistent for our rooms / reps.
Thanks!
What determines the start time of the campaign? OR - what determines when the campaign's day is half over - or the time that ADAPT_TAPERED begins being more strict about the max drop rate?
The reason I ask is - given consistent values for Average Agents Logged In, Max Dial Rate, Max Drop Rate, Actual Drop Rate, Local Call Times, and Latest Server Time - I have been noticing that some days, when we've over the max drop rate during the first half of the day (which is EVERY DAY

This system is (still) running SVN 2973, Vicidial v2.14-670a, BUILD: 180424-1521, DB Schema 1542 - so - if the rules have changed for this in later versions - I would be very appreciative if how is included in anyone's answer.
SO...if I knew what caused the system to think that the first half of the shift began - I might be able to control this a little better and make this too, more consistent for our rooms / reps.
Thanks!