Hi,
i didn't succeed to make your plugin to work. I failed creating the plugin or my commands are not right. When you run the check at beginning of every skill, is there anything else to write in the notetag before ?
'if user.isEnemy()
CHANGE SWITCH 1: on
else
CHANGE SWITCH 1: off
end '
Anyway,
I found another interesting way to resolve this - and I'm so happy that I want to share

.
1. In the Battle Engine Core plugin - change "Side Sprite Priority" to 0.
But the problem is : if ennemies and actors have the same Y, wich happens when one move to the other, then ennemies have priority and appear on the top.
2. In the notetag of your skills, add this to movement command : 'offset y+1'
So when the user of the skill will arrive in front of the target, the sprite will be 1 pixel lower, and so it will appear above the target. The only inconvenient is that it's not totally clean cause the sprite will move a bit - but just 1 pixel so it's pratically invisible.
Example :
NOTETAG SKILL n°1 ("Basic Attack")
<target action>
...
move user: targets, front, 20, offset y +1
...
</target action>
I hope it will be usefull.
Bye