I was wondering what recommendations for the attack angle of the nails on tremolo should be. I have relatively short nails and find that 30 to 45 degrees tends to sound muddy and straight on is harsh. Obviously, I notice a tonal difference with nail length as well as the angle so I thought maybe I should see what the recommendations on attack angle would be and see if I can change the nail length or technique to get that airy tremolo sound.
I think a bit more stright is better for tremolo. It results in more even distance from each finger to the same string, which results in more equilibrated sound. A bit more high partials also helps enhancing the sound of the attack and detaching the notes from each other, resulting in clearer articulation in such a fast notes repetition, specially to a listener in a distance when playing in a concert situation without amplification. Becareful that the sound from near is not the same than from a distance. Higher frequencies decay quickly while lower ones go further (as you can notice in a car passing by with loud sound speakers). So a bit more high partials might be welcome and the tone gets better in a distance.
You also can check John Williams, Evangelos Assimakopoulos and several others with a great and beautiful tone in this more straight attack. So there are ways to get less harsh sound with a straight attack, it is a matter of discovering the right way of doing it. I would say the way you pass finger over string, the speed and tip rigidity are important and sometimes negleted. Besides that, some very small rotation together with right nail shape is just enough to help avoiding the harsh sound of the fingertip center.