Just for your info re gaiters...
The 2016 onwards Triumph T120 also has 41mm Showa forks and has exactly the same extended distance between the underside of the bottom fork yoke/triple tree clamp and the top of the fork leg so happen to be a perfect (if expensive) fit.
you're English is superior to my French which I learnt over 45years ago at school and promptly forgot most of it
Here's my T120 on the side stand so its springs are compressed by the weight of the bike. I sadly need a third hand to take a photo with the forks uncompressed. But as can be seen in the photo there's around 130mm showing and there is 30mm that is not showing. Perhaps the T120 you checked was not standard which gave an inaccurate measure.