There are a few things that go into that score.
First is that the test is, indeed, adaptive. If you do very well on the initial questions, you will rapidly be rewarded with challenging problems--problems that are hard to get correct, but that have a large impact on your score when you do due to their difficulty.
Second is the fact that your percentile scores are a little misleading. The Verbal section follows a very regular bell-curve in terms of it's score distribution, meaning that your 94 %ile score is quite respectable, but several points off from the maximum. Conversely, the Math section is much more skewed to the extreme, and in all likelihood your 90 %ile score represents a larger raw score than on your verbal section, and therefore a larger proportion of your 800 points.
I hope this helps clear up any confusion--let me know if you have any more questions!
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