With HP scale, how about making the enemy START with a high HP calibrated for 85 players, and scale negatively, to lower the HP for a smaller group. This would make it far less likely things get instad by a massive group turning up before the correct scaling kicks in.
Instead of what I think we currently have: baseHP + (HPscale x playercount)
eg. with base 15 000, scale 1 000 per player:
1 person gets 16 000, 35ppl get 50 000, 85ppl get 100 000, 120ppl get 135 000
Negative scaling would be: baseHP - (HPscale x 85-playercount)
eg. with base 100 000, scale -1 000 per player:
1 person gets 16 000, 35ppl get 50 000, 85ppl get 100 000, 120ppl get 135 000
The above example is for an enemy that you want to have 100 000 HP for an 85-group and 16 000 HP for a soloer. This negative scaling formula even still works to increase the HP above base if there are more than 85. You can see from the numbers the HP outcome is the same.
Apologies if someone else already suggested this! Had a quick search but found nothing.