I think that might be a bit on the anthropomorphic side, but yeah, a mature male Amph cit/devil, can easily reach 13-14" over time. My male is now 10+ yrs old, and easily in that size range.
One thing I will add, is according to the research I have done over the years, Amphs from these bodies of water (crater lakes) spend a good portion of their time in a lair made out of rocks/boulders. They aren't exactly Mako sharks that cruise the shallows of the entire lake all day looking for prey. Far too dangerous for an Amph that wants to reach maturity.
I think back to my early yrs of bass fishing along the shoreline of the Detroit River, and species such as Rock Bass, and Smallmouth Bass. The largest, oldest, and most experienced fish, were found in the thickest tangle of underwater structure. Large rocks, or in my case broken up slabs of concrete along the water's edge, is where the largest and oldest fish were to be caught. And even then, I had to coax those older fish out with a live crayfish, hooked through the tail, and then fed down into the caverns. They didn't get to be that size/age by making the mistakes smaller/younger fish made. .
That doesn't make a 3ft tank a good long-term home for an Amph, but a captive bred fish that has never experienced open water, such as a large river or lake, IME will adapt quite well to most reasonably sized puddles.
