Airfix child myself Bezzo!
I only game in 20/25(8)mm & the rule is 20thCentury=20mm. A few ranges blur the lines eg My Zulu war stuff is 20mm Raventhorpe & 25mm Ral Partha- they are the same size.
I have to stick to these scales due to the large amount of scenery I have that can fit either
See you at Vapnartak?
Regards
Shaun