>Which hiatus are you referring to?
Both within words and between words. Examples include:
Vedic bhaas for Skt bha:s < *bheHes (noun type as in manas < *menes)
Vedic panthaam for pantha:m < *ponteH-m. (syllabic -m, hence -am)
Avestan mazdaam < *mnz-deH-m. (syllabic -m)
Vedic tanuah (not *tanvah), < *tnuH-os
and so on
I have a note (which I can't vouch for personally): "The Vedic forms are
archaisms, but Gatha Avestan is consistent in all cases where a laryngeal is
expected."
Another consonantal effect is the apparent exceptions to Brugmann's law.
You see this best in the Skt causatives. The usual pattern has *-o- in an
open syllable, so that syllable appears lengthened in Skt (e.g. Skt root
kr to scatter, causative ka:rayati < *koreyeti) But verb roots that end in
a laryngeal have an unexpected short a. The consonantal laryngeal means the
-o- syllable is closed, so it doesn't lengthen. For example janayati <
*gonHeyeti. You see the same effect elsewhere, e.g. in the second element
in compounds: aja-gara (goat-swallowing) < -gworHo, cf Greek compounds in
-boros.
Yet a third consonantal effect is when the laryngeal forms position for
verse (i.e. it makes a syllable closed, and therefore heavy in the
scansion). So savitar scans savHitar and duhita: scans duhHita:
Peter