Rooting Alien Dalvik on the Jolla C

First off, I want to say I'm sorrry for double posting this here and in the SailfishOS section! The latter section feels very empty and I'm not sure it was the right place to ask, since most of the knowhow is concentrated here. Should I get help here, I will update the post in the SFOS section.

As the title suggests, I'm looking for information on what is necessary to root Alien Dalvik (5.1.1 API lvl 22) on the Jolla C

On Jolla Phone, we had one superuser binary that we linked to in the directories opt/alien/system/bin and xbin and in /system/bin and xbin named su

The same procedure seemingly does not work. I've tried putting one of the many available su binaries in the respective places without success.

Sadly I have no clue where to look next. Does Android 5.1.1 need more than just the su binary for root access? On Jolla Phone Android 4.1.2 it was enough.

We have root rights from SailfishOS side, so we can place files anywhere on the system. Android apps still need a su binary and maybe more? Most threads here on how to root devices, describe the necessary steps, but don't go into detail as to what is actually happening beneath and what is actually needed.

Thanks for any help in advance!