10% to 80% seems like too wide a range for your range of “how many are on the largest instance” 10% means only 1 in ten users are on the largest instance and 9/10 are spread out on the rest, If anything that seems overly fragmented. On the other end 80% means 4/5 users are on the largest instance and 1/5 are shared between all other instances which is incredibly concentrated.

I’d sugest narrowing the range to 20% to 66%, 1 in 5 on the largest instance is still plenty dispersed to ensure that there is competition/variety and 2 in 3 users on the largest instance is already well into monopoly territory.