If it really is a short finger issue, as it happens. The only way to get the lever closer is to grind a little off the push pin. That is the little part the lever pushes on. Just take a little off at a time till you get it right.
You will not damage the clutch, in fact you probably need to burn the clutch in a bit for it to work properly. The Gasser clutch is quite touchy on clutch pack thickness. Go to a trials and ask the top riders what they run for oil.
After all this, have you tried running the bike with the gas cap off? It could not be venting properly. Every trials bike seemed to have venting problems in 2018 for various reasons.