Baseline alignment for scripts with hanging baseline

I'm a bit unclear about best typographic practice for baseline alignment in
scripts with a hanging baseline such as Devanagari and Gurmukhi.

I am not sure what the right terminology is, so I'll use the following
terms:
- top baseline: the continuous line connecting the tops of letters;I think
this is sometimes called Shirorekha
- bottom baseline: the bottom edge of the vertical stem, eg the bottom of a
character such as U+0915 (DEVANAGARI LETTER KA); I think this is sometimes
called Padrekha

Based on reading the OpenType spec (
http://www.microsoft.com/typography/otspec/base.htm), I had previously
assumed that everything was aligned using the top baseline.   But I am no
longer sure.

Consider the following scenarios:

1. Bold word in the same line as non-bold text; everything the same point
size (where the bold top connecting line is thicker than the non-bold)
2. Mixing scripts which all have a hanging baseline (eg a Gurmukhi word in
a paragraph which is otherwise Devanagari)
3. Initial drop cap
4. Initial non-dropped cap (ie the first cluster in the paragraph is set in
a much bigger size, but the second line of the paragraph is non-indented)
5. Run-in head: a paragraph starts off with a heading which is in a
slightly larger size than the rest of the paragraph

My guess is that 1, 2 and 3 are typically aligned using the top baseline,
but I'm unsure about 4 and 5.  I possess only one book in Devanagari and it
aligns case 5 using the bottom baseline. This makes good typographic sense
because it ensures that the distance between the first and second baselines
of the paragraph is the same as the distance between the other baselines of
the paragraph.

Another question: when you align using the top baseline, do you align using
the upper edge, the center or the bottom edge of the connecting line? I
guess the upper edge.

James