Hi chokeslamcena, I'm that "Xavi" from Coaster Critic's FB comments (also known as Jivo or Bloggercoaster). And let me explain you my personal experience until today, to make clear my views on Shambhala.
I tried it out on the third day of operation, when it's assumed that a problem like this should have been resolved but "oh god!" It turned out to be a little hell. I tried to ride on 3 occasions and in different rows and seats, being expelled from Shambhala in all this attempts. I saw too that in each cycle they expelled 3 or 4 people per train, so it was not an isolated case of me.
After a few days I could talk to other park workers and ride-ops from Shambhala that indicated to me that the park received hundreds of complaints every day about it and that the ratio of expelled people was 16% (between 3 and 6 people in every cycle).
Apparently the park made changes in operations and adjusted the harnesses, so I decided to try again a couple of weeks later and yes, I fit and could tasted the speed and hills of Shambhala!
Unfortunately that day it fell next to me a piece of metal (although in fact were two) and the park closed since then for a week Shambhala, apparently to change the lift chain and improve security of guests (there was some commotion on Twitter and Facebook, even Oriolat uploaded all the photos here, I think).
Fortunately, Shambhala now works perfectly (and great!) and it seems that the park has changed the measures of the seats to make it more "fat-friendly", although of course they can't violate the safety standards and probably still have people who can not ride it.
I only will give you two tips for your visit:
1) As fdelhomez says: don't pay a lot of attention to the test seat measures. The fact that makes you fit or not (if you are a little width of thighs) is really the effectiveness of the ride-op checking the harness, not really the sit measures.
2) The queue time in Shambhala is like a lottery. Maybe 10 minutes, maybe 3 hours. It depends on the number of trains (this is not Silverstar and they don't put on track the three trains from early in the day
), if the park is crowded or not on your visiting day (given that we are in summer season is more likely to be) and more random aspects such as weather or the cuts in operation (thing that is quite common in PortAventura).
Anyway, I think I've said all I had to say, anyway this week i will do a big review in Bloggercoaster so if you want more info, you know where to find it
Have a nice visit!!!