>1) In general, pre-PIE short *e, *a and *o (or some similar trio of
>vowels) merged. However, the distinctions were preserved next to
>laryngeals.
Not true. Based on Lubotsky, the *e *a *o* > *a in Proto-Indo-
Iranian preceded the disparition of the laryngeals.
Lubotsky supposed the following timeframes:
1. Brugmann's Law
2. Vocalization of interconsonantal laryngeals
3. Palatization
4. *e, *a *o merged to *a
5. *h1, *h2 *h3 merged to a common *H
6. Loss of laryngeal before mediae
7. Laryngeal accent shift
8. Laryngeal Metathesis
Best Regards,
Marius