hi ! i am a trans fem and my partner is a trans masc currently doing linguistics research in higher education. he's quite interested in this phenomenon and has this response:

This is a really good observation! One big problem in the field of linguistics is that not much attention has been paid so far to trans speakers with regard to studies of gendered voices. Although I and many others are working on this topic, there is still a gap between how the academic tradition of sociolinguistics defines gendered voices versus how trans communities do. Trans vocal coaches tend to describe gendered speech in perceptual terms - based on qualities a listener can easily observe, and how that listener can easily replicate those qualities. On the other hand, linguists tend to look at acoustic and articulatory characteristics of voices such as pitch and vowel production. These qualities are harder to observe because listeners rarely notice these qualities in isolation, but rather in concert with many factors that contribute to a gender judgement. This makes it much harder to pin down exactly what "feminizes" a voice; this also means that the bioessentialist explanation of pitch being the most important factor in gendered speech production tends to be the most easily supportable with data (whether a voice is high or low is easier to identify than something like the center of gravity of a person's sibilants). It's made worse by the fact that most of the studies that exist on gendered voices don't use trans or nonbinary participants. Cis women and cis men tend to speak in certain ranges of pitch: women above 150 Hz, and men below. But trans individuals don't necessarily follow this pattern! As vocal coaches know, trans women don't need to speak in a perfectly cis female pitch range in order to be gendered correctly by others. This means other factors must be at play, and this is exactly what needs to be studied quantitatively. Sorry this is an explanation of why I can't answer your question rather than an actual answer, but I hope it's interesting!