Do extensions and robot bonuses work additively or multiplicatively?

For example, I have basic robotics level 4 and extensive mining level 3.
So in an argano, i have +20% yield from robot bonus and +3% from extensive mining

I thought the 2 are multiplicative, so when mining stermonit, i should be getting 450 * 1.20 * 1.03 = 556.2 stermonit per cycle (assuming stermonit base yield is 450. right???)

But right now, i'm getting 533 stermonit per cycle, which is more like 450 * 1.23 (1.2 + 1.03) (= 553.5 stermonit per cycle). This suggests the robot bonus and extension work additively

Thing is, other threads suggest extensions work multiplicatively. So even if this specific mechanic is working as intended, how do i tell when extensions and bonus are additive or multiplicatively?