Can confirm 33 gives me +4, I believe that people with 31 wouldn't lie about it, so that's probably the case too. If 8 is indeed the base for +2, then 32 would be needed for +4, and if it rounds up then 31.01 is the minimum, or however high it needs to be to round up instead of down.
@basuranephilim "This page is outdated and reflects the Legacy Haven & Hearth world." Dont take info from Ring of Brodgar from granted, especialy when it has this note lol.