I had multiple blast injuries resulting in TBI and PTSD along with hearing loss and tinnitus
Provided that it's well documented by medical people and/or you have cf98s,plus a diagnosed condition (not a list of symptoms), then you should be good. I waited 7 months once my condition was deemed stable / chronic. I got 55% on the PTSD, 10% on the TBI, 12% for hearing loss, and 8% on tinnitus.
I had 10% for my back before that. I also have a visual issue that came up as a result of the TBI that I'm still waiting on...
As to how I was assessed - the bigger impact to quality of life and the need for ongoing treatment plays a factor on the amount.
For example, for mental conditions - if you require medication for which you are expected to need to function... mostly likely for years to come and be under the care of mental professionals - you will likely get a higher award. If your life can go on with little change or need for medical equipment or services... your award will be lower.
From my conversations with other vets in my situation - it appears that ptsd falls between 30 and 70% for most successful applicants. Normal process appears to be if it looks like you are going to require ongoing care and or your condition is not yet considered chronic or stabalized - they will award you 10% to start... and then once they have a better idea of your condition - vac will adjust the percentage and give you the difference. That's how my process went and I was in that position one year ago.