adjusting front forks height in triple clamps?
 

I am experimenting with lowering the triple clamps on mine xt660z tenere with pretty good results. I moved forks tubes up around 7 mm and bike is way more agile and responsive on tight trails, front wheel doesn't have tendency to wash out anymore on loose terrain turns. Lowering triple clamps we're basically decreasing the rake/trail of the bike so my tenere is closer now in these regards to more off-road bikes like ktm 1190 or 1090 Adventure R which have 26 rake, yamaha had 28 from factory. I think I will keep my changes.

On dirt bikes that's pretty common to make such adjustments but anybody tried this also on bigger adventure bikes?

You got the results you should have from that change, well done! The only caveat to that change is that it will also be less stable on the highway, and especially with a load of luggage. You may want to reset it back for that purpose, it could get VERY nasty. Enjoy it on the trails!
Other options are to increase spring preload in the back, maintaining ground clearance but losing a bit of travel - probably, unless the spring is too soft to start and needs a little more preload.

yeah, I read about highway issues as well but so far I tested it up to 100 km/h and no issues there. Also what surprised me some bikes like Triumph Tiger have very steep rake from factory, 23.7 degree and no reports about lack of stability.
More like sport bikes actually, so I don't think so decreasing yamaha factory 28 degrees a bit will be a problem in any conditions. Even bmw F800GS has 26 degrees rake, probably that's why feels more nimble then tenere. Regarding the preload, I have progressive springs on my xt and it works best with minimum settings.