JW, most peoples yellow flags (iris) don't get bigger than three or four feet! I have given chucks away and those chucks don't seem to get as tall as the one in my pond. Different growing conditions affect the plants height. If you have all day sun, the plant will only get about three or four feet at the most. If your chuck is dense and large, the plant will grow taller too, to reach the sun.
My pond gets morning and some afternoon sun, but not all day sun, so the plants grow very tall. When the plant gets very tall they tend to bend over at the top.
JW, about your sweet flag, it is known as Acorus gramineus. (Japanese rush or otherwise known as dwarf sweet flag)
It is hardy from zone 6 to 11.
My sweet flag is Acorus calamus. sweet Flag, zone 4 to 11.