APACHE SetEnv directive (from .htaccess) not send to CGI process

I don't understand Apache2 mecanism in this scenario :

1/ In this location : var/www/cgi-bin/ (user's group rights : www-data)

i've a CGI script (php-cgi) who will execute PHP app + VAR environement version :

#!/bin/bash
# file : var/www/cgi-bin/cgi-php
exec "/usr/bin/php-cgi$PHP_VERSION"

This script have : chmod a+x executed at runtime by user www-data (Apache server)

All PHP versions are located in :

/usr/bin/php-cgi5.6

/usr/bin/php-cgi7.0

/usr/bin/php-cgi7.1

/usr/bin/php-cgi7.2

All versions working fine.

2/ In Apache Server .conf file, i use :

    Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
    Require all granted
    AllowOverride All



SetEnv PHP_VERSION 7.1
ScriptAlias /cgi-bin-php/ /var/www/cgi-bin/
Action php-cgi /cgi-bin-php/php-cgi
AddHandler php-cgi .php

When Apache2 restart i can see in http : PHP Version 7.1 loaded (works fine).

3/ If in .htaccess file i put another PHP_VERSION variable, this not sent ??

File : /var/www/html/.htaccess

SetEnv PHP_VERSION 5.6

In this case .htaccess file do nothing at all.
In http i can see : PHP Version 7.1

Question :

Why SetEnv PHP_VERSION X.X at runtime is working (when i start Apache2).

And why i can't set a new variable (SetEnv PHP_VERSION X.X) from .htaccess file ?
I think Apache won't send $PHP_VERSION variable to the shell environment (Ubuntu Server 16.04).

If anyone can help me...
Thanks a lot.

Source : https://www.codejam.info/2014/08/apache-get-php-version-from-environment.html