Creature picking on encounter algorithm?

fot1

Hello. So today I was testing encounters, and how they actually spawn. So I had setup an encounter with a couple of 0.33 CR creatures, and three 2.0 CR creatures. I've set the encounter difficulty to normal, and loaded one level 4 char. It spawned 3 0.33CR creatures. Changing this to Hard, it spawn 3 2.0 CR and 3 0.33 CR cratures.

At first I tough the CR of the first encounter was 1.5, and the second 7, but then I realized that maybe the encounter CR is not a simple sum of all monsters CR. Yet it scales waaaaaay to quickly from normal to hard. So, I wonder if I did something wrong?

Is the formula/algorithm to decide which creatures will be spawn somewhere?

Thanks!

fot1

OK, I found this pretty good guide: http://www.nwn2toolset.dayjo.org/Design/Building_Challenging_Encounters2.pdf

(I'm also attaching the guide here in case the link goes offline)

The autor actually took the bullet and did a big experiment (as I was thinking on doing myself, thanks god I found this before). It shows experimentally that the encounter CR is actually the average CR from the creatures + 1 per spawned creature. It also shows that the CR for normal is CL-3, hard is CL+1 and impossible is CL+5. More details on the document.

Looking on my original post, it actually fits the hard encounter (average CR is 1.16*5 = 5.60, my CL is 4, so 4+1=5, close enough). However it does not work on the normal encounter. I assume that the calculation is actually different when the average CR is less than 1. I can imagine that instead of sum +1 per enemy, it sums the CR (in this case, 0.33). So, the actual calculation would be average cr (0.33 + 3*0.33 = 1.33. Expected was my character CR 4-3 = 1, so again, close enough.)


So I speculate that it might be different when more creatures are spawn (for instance, +1 up to 4 creatures, +2 for the 5th and +3 for the 6th, or something on those lines) and in really high or low CRs. Would be great if someone from beamdog could give a quick look in the code and describe any corner case that is being missed.