The scoring is indeed based on angle, following the racing line perfectly and speed. Theres a limit on the angle thing tho, backward entries wont give you extra points - over 80 degress you're playing with fire, it ends with 90 degrees i think, counts the drift as a spin.
But thats why the people in the top are in the top - They do everything over and over until the get the perfect run. And they use specific cars for the points thing...
Dont measure your drift in points though, GT5-s points system is pretty bad, the guys who are in the top10 are all with controllers and they have no real style in their drift.. Neither they could tandem.
The real guys you should look up to are the ones famous in this community for their tandeming godness.. Like monsterGAUZ, fadam and some other guys.