It’s a bit more complex than that.
- Each item has stat scaling factor, which can be zero.
- Each affix and relic completion/craft bonus has it’s own jitter, which can also be zero.
- There are non-scaling stats (e.g. % exp increase or flat energy regen), stats with fixed scaling that ignore item stat scaling factor (e.g. % crit damage or % cooldown reduction) and fully scalable ones that depend on both item stat scaling and jitter if it’s non zero (most of the rest) — that’s my personally classification, but you get the idea.
The resulting stat value is calculated based on stat scaling factor and jitter if the stat is derived from affix/bonus — this means that the same affix for the same item category (e.g. one of gun affixes) can produce different min-max range for its stats when it is applied to items with different stat scale factors.
Btw, the fact that %OA or %Armor scale so little is just because of the small values, which is usually something like 2 or 5, because e.g. 3+10% scaling is 3.3 which is displayed as 3 cause it’s rounded.