Horizontal BnZ doesn't work because of the insane acceleration due to using boost.
For exapmle: I can achieve an extra 200km/h of speed in level flight in my Ta-152. While in most cases below T8 acceleration isn't that extreme, it has a similar affect. Couple this with a halving in the time it takes for most planes to perform a 180 and you will be well within gun range as you try to boost away.
On top of that, something screwy is going on with the horizontal space in the game, it's compressed so that you have to be going faster to cover the same amount of distance as before 2.0. However, gun ranges are still calculated at an absolute value (this effectively makes gun ranges greater).
As MARS said, the best technique is to fly just below the red line of your altitude, perform a medium angle dive on your target and zoom away level while boosting or in a slight dive. While your HP will be preserved, the technique does not lend itself to the capping of sectors the current meta of the game..