My Sirrus has the same 3 X 8 drivetrain with the Shimano Altus front derailleur...
It is fussy to set-up but once "dialed-in", even though it's an "entry level" component, it works very well!
Here's a link to the Owner's Manual that I found helpful.
The highlighted "tip" on page 11 solved my problems... (closer to 1mm vs 3mm, for my set up)

Sounds like you know what you are doing... (but it is a"frustrating" adjustment - took me 6 or 7 "tries" LOL!) Good luck!