Interesting point. "A bit/drop/dash/hint of" is accepted in Ximenean circles (e.g. Azed) to mean, by convention, the first letter of a word. It does seem a little incongruous, considering that "by convention" usually isn't enough to justify something to Ximeneans (of which I am one!) unless the grammar/logic supports it (that's why Gateshead = G is right out, even though it fools nobody).
By contrast, I remember that Araucaria, especially in his later puzzles, often used "a bit of" to mean ANY letter, or sequence of letters, in a word. E.g. "a bit of pumpernickel" could be P, U, ML, ICKE etc. I'll leave it to the mathematicians to work out the number of possible combinations!