Can synizesis happen when the perfect stem ends in 'u' and the ending starts with a short 'i'? For example, can the 'ui' in fuisti be synizesized1 into a diphthong? In my understanding the two vowels would normally be in different syllables. If it is normally a diphthong — which I doubt — can it be split in two?
What I would like to see is an example or two in classical poetry showing this synizesis. If no such example can be found, then something like "I looked through the Aeneid and found no examples, but there were these cases without synizesis" would make a good answer.
1 I am not sure if this is the correct verb in English. I formed it by analogy to "synthesis" and "synthesize".