I didn't think it was crazy big, but I looked at mine I got from Bizarre Botanicals.
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There's a couple of mature ones in there. The top one is much more erect growing with shorter petioles, while the bottom one is more leggy with longer petioles. The bottom one almost spans the entire four inch pot.
Then I compared them to my seed grown typicals
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Lots of variation in petiole length. Sown this spring, plant size ranges from ~1 inch to ~3 inches, with obvious differences in petiole lengths.
Then my tropical intermedia
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Pretty uniform in size, ~1 inch, but some slight differences in petiole lengths.
It's most likely just differences in genetic expression, much like different VFT characteristics.
However, mad scientist time, maybe one could selectively breed long petiole to long petiole over and over to eventually get a 12 inch wide intermedia. See how far the genetic expression can be stretched.