6k energy is incredible! This sounds to me like getting at least 2 other rare campaign champions on that day, before you even started to farm stage 4. But then, you kept pushing, despite the absence of success?
In my experience (from farming experience, how funny yaya👆) do I get two or four rare champions in average, exceptionally up to seven rare, along my champion training per !day, while the rates of the individual drops hold up with given informations of Rhbobo.
The usual energy consumption varies from 700 -1700, with rare peaks up to 2400.
But keep in mind: most relevant is not the energy consumption nor is the drop-rate. - Imao! - has raid a lot of hidden mechanics, and one of them seems to determine the drop-chance in reference of champions you already obtained during that day from campaign.
Hereby, a day is meant to be the time between two server “restarts”, regardless of local timezone.
I witnessed several times situations getting two rare champs within the very first hour of farming, but then not a single drop during therest of the day.
Sometimes I got 4 rare within four hours. But afterwards, none other drop while farming experience for another eight. But the most laughable: during some intensive farming seasons over several days did the trash-hold of my account raised so high that I got two rare champions right on the first two runs after the server restart! And the same thing happened the day after XD.