I've been shooting this bullets for several years so it's not like I went out once and these are the numbers I've come up with. .630 G1 BC works all the time, everytime for me.
If that works for you every time and you're happy with it, then you should carry on. But, it does't mean that .630 is the correct BC. (and, I don't think you made such claim)
It's almost certain that something is amiss in your software or inputs.
The important thing is that you're happy and successful within your own shooting discipline.
Meanwhile, I'll keep dreaming of a .630 BC bullet that will shoot well in my 25-06.
With a slow twist, mine really favors 75-90 grainers. But, it gets they job done.