[O] Latex image placement (...again. H vs. h!)

[John Hendy]

Was just rediscovering how to properly get floats to drop in where I
want them in LaTeX export (right where I say vs. where LaTeX thinks is
convenient). I knew I'd posted on this about a year ago and was trying
to search for the thread. In the process, I came across this from the
manual [1]:

,---
| To modify the placement option of the floating environment,
| add something like ‘placement=[h!]’ to the attributes.
`---

Now, I'm not sure what all the options are, but this didn't work for
me. Only [H] properly dropped my floats in where I wanted them. Is
there a reason for this? In looking in wikibooks, they seem to
indicate that there are a few variants on the "here" option: [2]

,---
| h: Place the float here, i.e., approximately at the same point it occurs
| in the source text (however, not exactly at the spot)
|
| !: Override internal parameters Latex uses for determining "good"
float positions.
|
| H: Places the float at precisely the location in the LaTeX code.
| Requires the float package,[1] e.g., \usepackage{float}.
| This is somewhat equivalent to h!.
`---

So, does my need for [H] mean that LaTeX just really, really, really
wanted to space my images differently than I wanted? It does seem like
h! *should* work based on the wikibooks description, but it didn't. Is
[H] the only absolutely positive way to make sure floats are right
where you want them based on the surrounding text?

Thanks,
John

---
[1] http://orgmode.org/manual/Images-in-LaTeX-export.html
[2] http://en.wikibooks.org/wiki/LaTeX/Floats,_Figures_and_Captions