Bacnet 22 gauge and 18 gauge

The BacNet system uses a 22 gauge three conductor wire. Objective: extend loop in order to install another control cabinet to add another trunk for future, this is what the Client wants to add.

I had the idea of using an 18 gauge because we didn’t have extra 22 gauge.

My foreman tells me that it would’ve been wrong to use it because it would mess with the signals and the system wouldn’t function properly .

My reasoning was save a little money and upgrade the wire (of which we had in stock) to 18 so that there wouldn’t be any voltage drop and better signaling because of less resistance.

So my question is was he right?

The only reason why I ask the question is because he always stretches the truth and he always wants to be right and he hardly admits when he’s wrong, which is why I’m asking this question and sometimes I doubt myself.