Welcome to the Uphill Athlete community. Thanks for writing in with your questions. It looks like you did a good job on the test itself. I suspect the reason for the lower drift in the second half of the test is that the first half served as a better warm up. The aerobic system is very slow to come on line and it this was a cold day you probably needed a longer worm up.
I’d say that 149 seems like a good place to peg your AeT (top of Z2). The best test will be; can you get up tomorrow and do the same run you did today and then again the next day and the next? If you can recover in 24 hours then you are probably using a a good AeT. As you see improvements in your daily runs (based on perceived exertion, pace etc) you may want to retest in a few (6-8) weeks.