Anal gland question(s)

[xcaer]

Okay, so I have a 2.5 year old Shepherd/Akita mix, Eli.
He was recently on antibiotics for a skin issue, and it caused soft stool for awhile and in turn, I ended up having to express his anal glands. He started getting the tell tale fishy smell really bad, but no obvious signs of discomfort. I got a bit of the lovely smelling fluid out, and the smell went away. I did not completely empty them though as I was fairly new to the manual express thing.

Now, I just recently expressed them again (3-5 weeks after the first I think?) because he's had terrible gas, and he's been on a newer, much better quality diet, however it's not very high in fiber so I've been supplementing with 2.5 tsp of ground flax twice per day which has bulked his stool up quite nicely, but it's still not as firm as I think it should be in order to express naturally.
Again, he had no obvious signs of discomfort. No scooting,licking/chewing,not super smelly, but just smelly enough that when I was checking his tail(where his skin issue was, as it requires regular cleaning still) I could smell it. Got quite a bit of fluid out, but again, not completely empty.

Now my questions;

How empty should a dog's anal glands be exactly? I know the fluid is meant to aid in lubrication while having a bowel movement so I'd assume they shouldn't be completely empty, but how much is too much, or how little is too little?

Also, what can I give him to firm up his stool?
I don't want to create MORE stool which is what the flax(and fiber in general) does, I just want to firm up the poop so he can express his glands naturally. His stool isn't loose or anything by any means, it's well formed and such, but it's clearly still too soft for him to express naturally.