Indesign not honouring cell inset

Hi!

I have set my right cell inset to 0.5mm but indesign is still pushing the text onto the next line when there is more space (or it goes overset if I set the cell height to exact). I have also tried setting the right inset to 0mm and 0.1mm and am getting the same results.

Please see attached screenshots - there is definitely room for the second 'm' on the same line in the same cell!

I tried creating an extra column for the mm measurements and merging the two in the top row for the needles title, but the same problem is there so the numbers had to be too far apart.

There will be a lot of these tables across multiple pages so I need them to be as tight as possible!

What am I missing?

Thank you!