[BAracer]

Slot.it, Slotting Plus and MR Slotcar are all gears I use in Scaleauto pods.

There is a golden rule fie matching teeth spacing across all gear manufactures.. 

Ideal gear teeth number = diameter of gear times two and then minus 2.

So... 9t pinion are often 5.5mm in diameter because 5.5 x 2 = 11, - 2 = 9.

And your current 28t AW gear is within the 10% margin  of flexibility of this calculation

15.8 x 2 = 31.6
31.6 - 2 = 29.6 

The further you go beyond the preferred number for pinion or AW, the noisier the gears will be due to unavoidable meshing errors.