Final grade system (taught Masters) Edinburgh Napier

Hey everyone,
First time posting! 🙈
I have just found out that Napier doesn't use the credit weighted system for your final MSc grade.
Basically, they say you need a Distinction in 120 credits or a D3 or above in 80 credits to get a distinction overall.
I have a distinction in 100 credits (all modules but one) and I am currently doing my dissertation which is 60 credits.
So I emailed asking what I needed to get in my dissertation in order to get a distinction overall (I figured I had some wiggle room because I already have a distinction in 100 credits).
I was told I still needed a distinction.
Enter - confusion.
So I questioned it and was told it isn't a good system, but it is university wide!
So basically, I am in the same position as someone who got a distinction in 60 credits, despite having 40 credits (two whole modules!) more.
I cannot think of a more unfair way to decide a final grade, or am I mad?!
I've worked SO hard and on a serious note, I'm pretty gutted.
Do other uni's do this? Is it a Scottish uni grading system?
Would really love to hear from anyone.
Thanks.