...
How it actually works, as opposed to how you see a 'ramp', is that your payouts are simply spread out over 5ND which is currently about 3 days.
You get paid for each share you submit, over the 3 days after you submit the share.
What this does is reduce the variance in your payouts.
Something like this if you think of it as submitting a share (s) each block:
s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+
If you consider the + to be the reward points when we find a block, the 5ND is simply the time it takes for the overlap of all '5' shares
Of course you keep submitting shares, so the gap appearing at the bottom doesn't begin until you stop mining e.g.:
s----+-----+-----+-----+-----+s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+s----+-----+-----+-----+-----+
s----+-----+-----+-----+-----+s----+-----+-----+-----+-----+
The height/number of '+'s is the relative reward.