I've managed to confuse myself about which syllables to stress in prefixed verbs of two syllables, the first one being short (e.g. circumdare or alloquor). Do I stress the penultimate syllable in each as if it were two separate words (CIR-cum-DA-re, al-LO-quor) or or the antepenultimate syllable as if it were one word (cir-CUM-da-re, AL-lo-quor)? Allen doesn't seem to have anything about this. A vague memory that pessumdare is stressed on the antepenultimate makes me suspect that the latter is the right choice, but the memory could very well have been implanted by aliens.
The Arch poet (c1130-1167) wrote a mock confession to his patron, Archbishop, and Arch-Chancellor to Barbarossa. Because his verse here written in stressed trochaics, Odds are stressed and Evens unstressed (except for the last syllable before the double bar-line)
In these 3 examples distinct prepositions(Bold) are all stressed, but prepositional prefixes(Italic) are unstressed -
Estuans intrinsecus // ira vehementi
in amaritudine // loquar meę menti:
factus de materia // levis elementi
similis sum folio // de quo ludunt venti.
Meum est propositum in taberna mori,
ut sint vina proxima // morientis ori.
quaero mei similes et adiungor pravis.
(I seek out those like me, and link up with bad people)
These prefixes have all been prepositional, describing time or place or agent; but when the prefix negates the meaning, 'im-,' and 'dis-,' are stressed.
via lata gradior more iuventutis,
implico me vitiis, immemor virtutis,
"On the broad path I step (as is the way of youth);
I get myself involved in bad stuff, unmindful of virtue."
Praesul discretissime, veniam te precor:
"Your most discrete Excellency," in the vocative. The negative prefix is stressed. "...may I visit you please."
These rules are not totally reliable; but these Pronominal prefixes are almost all proclitic, and the main stress stays with the object.