Field dependancy : display a textfield dependant from a custom multi-enum

Hello there !

i'm building a new project under Sugar Pro 7.5.2 and i'm meeting some difficulties : 

What i have and what i would like :

I have created a muliple choices dropdown, and a textfield.
I would like to display the textfield only if the user choses a specific value of my multi-enum dropdown.

So normally i would do that through studio, with the dependancy formula.

What i tried and what failed :

But there is a problem : my multi choice dpdwn is not showing under the Fields column in the formula editor. And even if i try to add it manually in my formula, i have an error of "field unrecognized".

So, how can i display a field on a Multi select field dependancy ?

I did not find any tips or tricks in my Community search, i even found martin peet being unanswered :
Using a Multi select box as dependancey criteria

it's been one year !

Please, tell me if i'll have to do that by code, and how.

Have a nice day ! :)