How to set persistent data path to sdcard on android

Hi all, i'm developing an app for android (galaxy tab s2) full of videos, and i run out of internal space quickly. my player setting is: install location: prefer external write access: sd card

this was fine without the sd card, so the persisten data folder was: android\data\com.mycompany.myapp on the internal storage. And i thought that just inserting an sd card could do the trick. but the problem is that when i deploy the app from scratch, the com.mycompany.myapp folder is still created in the internal storage, and not in the sdcard.

What am i doing wrong?

thank you all