Brix will often concentrate in one location of the fruit -- usually the lowest spot with regards to gravity. On tree ripened fruit, the sweetest part will be the bottom. On fruit that's been ripened indoors, it will be the side of the fruit that's facing the counter. Same thing happens with other fruits, such as guava.
In general, this year was a "low" year for mango flavor. Fruit flavor varies from year to year based on climatic conditions. Mango brix has been lower across the board this year. I think it has to do with a) all the rain we had early and b) the lower than average temps we had throughout spring. Someone on the forum also attributed it to the overcast conditions during late spring.
Also, mango flavor can vary subtly based on the conditions during harvest. For example, a mango picked right after a big downpour will be slightly more bland than rain picked during a dry spell.
Lastly, the earliest fruits of a mango harvest will normally be bland. So, for example, if a tree bears fruit from June 1 to July 1, the fruit harvested towards the end of June will be much sweeter than those harvested in the first few days of June.
PS -- you can actually view these differences with the aid of a refractometer. One side of a fruit might have brix at 18, while another side has a brix of 15 - 16. Bit once you get above a certain brix level, the human tongue has a hard time distinguishing the brix differential. So this phenomenon is generally only noticed in fruits with low brix levels.
