I'm not sure where you're coming up with that THCa to THC conversion of 33% to 11%, but it's more like a 10% differential (ie: 33% THCa = 30% THC).
There is no set rate for THCa to THC conversion. The answer is "it depends". Smoking is NOT the most efficient way to convert THCA to THC even vaping is more efficient. I've read estimates that range from as low as 20% conversion rate depending on how it's done. Sunlight I believe will convert about 20%. Weed like Acapulco Gold were "Gold" from the way they were cured in the sun which decarbed them. This is why when the scientists say weed back in the 60's was only 4% and at the same time people will claim that the bud back then got them more stoned. The fact is that most of the conversion had already taken place and the 4% was actually more like the equivalent of 12% or even more, again "it depends".
THCA will even break down into THC with no help at all, but it does so over time and VERY inefficiently. (eating absolutely fresh bud wont' get you high, eat old brickweed and it will. (That doesn't seam logical but it's true) I highly doubt there is actually a way to get a 90% conversion rates unless you are talking about absolutely ideal circumstances. Meaning it, would have to be perfectly fresh bud that's THCA hadn't already been converted by time or handling at lower efficiencies and remember the type of combustion matters too.
And I wasn't trying to say that it's a set conversion rate of 30%, I was simply using that % as a hypothetical so that people would understand the concept. THCA is not THC it won't get you high and how it's converted into THC matters A LOT more than people think.
What I'm saying is that even though a lab might show results as high as 35% there is no way to know how much of that will be available once it's been handled, gets a little older and after the loss to combustion. I think we all understand this to an extent without even thinking about it. We know that fresher weed gets us more stoned but why? It's because the THCA broke down inefficiently.