Perfect Speaker Placement - Put next to the back wall as much as possible.

I would put a bookshelf in the back half, stocked with copies of Robert Harley's The Complete Guide to High End Audio. The article you cited can then be printed out crumpled up lit on fire and used to light your barbecue. Might as well get something useful out of it.

Isn’t it written by the world class professional studio engineer? I thought that it’s professional standard. 
Any industry insider?

It’s interesting that there are two completely different ideas. 
https://proaudioblog.co.uk/home-studio-monitoring-speaker-placement/

Just to be clear, of course things are dependent on situation. Many speaker manufacturers recommends equilateral triangle set up as the starting point yet notably the engineer of Harbeth recommends a 1:1:1.5 triangle shape. 

The best part about speaker placement is that it cost zero to try for one self. 

Ignore Millercarbon’s comment. He would never let someone else’s obviously superior knowledge get in the way of his bravado. Odds are he didn’t even read it.

The article is targeted at near field monitor usage with emphasis on accurate frequency response for best mixing. Pretty much the article is spot on. Many audiophiles who have no clue how acoustics work just parrot others rules of thumb. Getting the speakers far into the room, in a small room, is one of those. This article explains why that is often a problem, but also says you need both acoustic treatment AND equalization to fix the resulting placement, but at least the final result will work properly while a speaker far from an untreated wall will leave you with a result that can’t be fixed and even if treated may not work properly.

It’s a good article in my opinion.

Just read the other article. They pretty much say the same thing and both are good. This was the one in your replies.

In Ethan's section on Real Traps he says 38% rule from front or back wall and then clarifies that's purely theoretical and is best measured.