Voiceless Aspirates

The voiceless aspirates in Indo-Aryan derive from a sequence of
stop plus laryngeal that later became a unit phoneme. Before
doing so, the first vowel in such words as the following should
have been long by position, should it not?

prthus 'broad, wide' < *prt-Xus
vyathate 'trembles' < *vyat-Xa-tay
rikhati 'scratches' < *rik-Xa-ti

So then after the change of the cluster to a unit phoneme, should
there not have been compensatory lengthening in the first vowel to
preserve the metric structure?

David