I have a question. Why 5ND? I like it cause I keep getting paid even when I have to stop mining, but why not 2,3 or 4? Just curious. Thanks
Edit- Also has it always been 5ND from the start? Will the number change based on future pool size? I'm done now

I don't like (and I guess most don't like?) mining and getting rewarded nothing for it

5Nd means it takes a > 500% block for that to happen.
CDF:
0.99326205300091 500.000% 1 in 148.4
So back when I changed it, 148 blocks was quite a while, so was rare.
The 'unfair' way I changed to 500% at the time was to the advantage of the people who didn't leave the pool when I changed it.
Making it higher means the 'abstract ramp' takes longer.
Again back when I changed it, the ramp was longer.
The number itself simply reduces the reward variance. The bigger it is, the lower the variance.
Too big means it takes too long.
5 seemed a good middle ground.