I am surprised no one has yet pointed out one of the most obvious considerations: having the tonearm parallel to the record surface tells you very little as far as wether the STYLUS is resting in the groove at the most desirable angle. As has been pointed out, attention needs to be paid to alignment/centering of the cartridge's coils; but, that does not necessarily guarantee that in that position the stylus will, likewise, be in the ideal position. Bottom line? It's a balancing act of various parameters, each of which will affect the resulting sound differently. So, experiment, experiment, experiment!