The rule says if a group is made of 3 or less player the APL should be minus 1.
What if we have three level 1 characters... i guess it is still APL 1 in this case?
Sounds stupid but i just want to make sure.
This has come up before. I always went with one step lower so that would be 1/2 as there are CR 1/2 critters. So, two steps down would be 1/3. See the section on adding NPCs for the progression.
If this reduction would reduce a creature's CR to below 1, its CR drops one step on the following progression for each step below 1 this reduction would make: 1/2, 1/3, 1/4, 1/6, 1/8.
I see no reason why the same progression wouldn't apply for APL.
The big problem with designing adventures for small groups is that they are often short one base class (no healing, no magic, no rogue, no melee). The other problem is that even a small amount of bad luck can put the party in trouble.