"IMHO, it's extraordinarily unlikely that Porter had the first dummy put together to cause the Confederates to blow up the INDIANOLA, though that's exactly how he makes it sound. (How prescient he was!) I can't remember where I came across it, but I read a much more believable account that the fake ironclad project was a result of observing the INDIANOLA's passage of the Vicksburg batteries, and was purely intended to make the Confederate gunners waste ammunition (and with luck, maybe burst a gun or two). The INDIANOLA's loss to the South was strictly an unforeseen side benefit."

This isn't just your opinion. This was a fact stated by Porter in a letter to a New York newspaper shortly after the incident. Apparently, when he was writing his memoirs years later, he either forgot, or figured everyone else had forgotten, what he had said in that letter. When the dummy was built and sent downstream, Porter was not even aware that the INDIANOLA was in trouble, much less captured. And notice that I said "when the dummy was built," not "when Porter built the dummy." As you have pointed out, just because Porter takes credit for something does not mean he actually had anything to do with it.