My original idea turned out to be false.
Sorry.
The Correct Version
TL;DR - Hunting progress is based on the effective energy after multipliers, regardless of when and how you used it.
From the discussion in the replies combined with comparing logs I learned that the effective energy after multipliers will always end up about the same, and the skill gain will follow accordingly.
My question was to what degree you can optimise the raw energy before multipliers. Can you gain an advantage from the earlier sessions, because their effective skill gain is much higher? Or will it always at best be "energy / 5" (World Tiger Day) or "energy / 6.25" (WTD + Meat Warehouse) at every point of progress?
I compared my logs to those linked in the MightyGoober guide, and the effective energy stays more or less in line (I only have data until the 50 merit). This means that, for the 50 merit, at best you used 2k raw energy (8+ Xanax), or at most over 13k energy (~53 Xanax). Until I can see logs to prove otherwise, anyone who claim they got the first merit at 1k energy must be lying.
Impact
In other words, here are three options for reaching the 100 merit. All of them have the same effective energy.
No perks: 164,800 energy or 659 Xanax. The equivalent of 31.4 weeks of 3x Xanax per day.
World Tiger Day: 33,000 energy or 132 Xanax. The equivalent of 6.3 weeks of 3x Xanax per day.
WTD + Meat Warehouse: 26,400 energy or 106 Xanax. The equivalent of 5 weeks of 3x Xanax per day.
...
Below is the original incorrect idea.
Advice
My best tip for beginners would be: never ever hunt, not even once, not even to try it out to see what happens. If you want to get the hunting merits without losing your sanity you have to get it right from the start.
Why? Because the amount of hunting skill that you lose by doing the wrong thing could be enough to ruin any future attempts at gaining the three hunting merits forever, unless of course you don't care about gym gains.
What I'm saying is that this is the one area of the game where trial and error gets punished.
Explanation
I'm sure we've all seen MightyGoober's World Tiger Day guide, but what I realised from plotting my own hunting skill gain is just how much hunting gets worse for every incremental attempt, especially the first couple of attempts.
Have a look at the following chart.
[image: i.imgur.com]
The blue dots represent every individual hunting session (vertical numbers on the left), and the red dots the accumulated hunting skill (vertical numbers on the right), currently at 52.
EDIT. Even though it appears like the lonely couple of blue dots on the left were wasted on regular training, the formula for the red dots will auto adjust based on your current skill level.
Did you notice that lonely couple of blue dots on the left? Well, before I knew any better I used 120 energy (or 12 hunting sessions) just to see what hunting was all about.
That's not a lot, right?
Wrong!
This mistake cost me a lot of skill. These first 12 regular sessions gave me a whopping 4.1976 skill. At a rough estimate, I could have had 17 additional skill if I did it on World Tiger Day (4.1976 * 5 = 21), or 22 additional skill if I also had a job at a 7* Meat Warehouse (+25% = 26). That's almost one more merit at no extra cost.
In summary, if you intend to ever get the three hunting merits, make sure you always have every possible perk. Ideally you should not even think about hunting before you are comfortable to get into a 7* Meat Warehouse (at least 3 days before the event). And then, when you are ready to burn some energy and sacrifice your precious gym gains, only then should you head over to something like MightyGoober's World Tiger Day guide or Torn's hunting wiki to prepare.
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Logs
If I could get hold of the logs of someone who either never did a regular hunting session or at least did their very first batch of hunting on World Tiger Day it would really help to clear up any debate on whether or not you actually get punished for doing regular hunting sessions.
You can use the Activity Log filter & export script to easily export all your hunting logs.