https://www.w3.org/TR/css-inline-3/#initial-letter-styling

Example 7 shows a case where the size of the initial letter is less than the sink and states that the alignment would be on the alphabetic baseline only. The effect is ugly and 'wrong'.

In this case, the alignment should be at the top, leaving any gap below. The use case is in trying to emulate letterpress printing in which only a limited set of discrete type font sizes was available to the printer. It makes no odds in setting up the type in the chase (I have actually done this, long ago) whether the initial letter type character is packed above or below, so it would have been packed upwards for the sake of appearance.

As a secondary suggestion, if initial-letter could have another value, to specify the initial letter font size (as, for example, a multiple of the surrounding text size, or with a keyword to indicate that the <number> value should be so interpreted) the effect would be easier to achieve and would base an 'over-sunk' character on top alignment only, so making the complex height calculation unnecessary in this case.

It may well be that the effect I suggest could be achieved in CSS by other means, but initial-letter should include it as that is the
obvious place to look.