Small tank was 14,000, large tank was 26,500. The biggest problem with setting tanks is what the hole looks like, and what the ground is like. If they have too much over dig, you are in trouble. If they have to be set from the end instead of beside the tank, you run out of chart fast. If you have to spin the tank, because they have it loaded the wrong way on the truck, that can cause issues. Its tough to get far enough away from the hole, so you aren't sliding into it, and yet be close enough to the edge, to have enough chart to set it.
Minimum for me for most tanks is my old tms 300, which charts like most 50 ton new cranes. I hardly ever set them with my 25 ton, which would chart out real similar to your boom truck. I find that by the time I'm far enough from the hole to not slide into it, I am out of chart. In rare occasions, you may be setting on poured concrete replacing a old tank, but even that I don't like to be setting on the edge of. I have tandem set tanks with a big excavator also, you need a good excavator hand though, they aren't made for precision setting, but for cycle speed.
I was probably 45-50' from the far tank, and around 30-35' from the close one. I usually figure 1' away from the edge, for every 1' of depth of the hole, I don't mind being closer if I'm setting on solid rock (which can happen in my area), but I've been on some really loose soil before, that the 1:1 wasn't enough.
Years ago I had ground opening up around the outriggers, when I got a big fiberglass water tank in the hole. THAT's a really bad feeling when you start seeing the cracks appear. They wanted to move that water tank a 1 1/2" to the west after I got it set down, and I informed them it was staying where it was, or they were getting a bigger crane. It was on black dirt, with a huge overdig. I got as far away from the hole as I could, for what I had for crane, and the soil conditions barely held up enough to get it in the hole. I was living in Iowa yet, and their good black dirt grows great crops, but it sure won't hold up weight.
Usually the tanks don't have the picking lugs clear at the ends either, that can mess you up with not being able to put out enough boom also. Most holes are at least 10' deep, so 10' away, plus 12' to your outriggers, plus 10' - 15' to the center of the tank depending on overdig. So you're looking at 30-35' radius most of the time, and that's what you have to be to spin most 45-50' tanks. Or to get them off the truck if the truck has to back them up to you. And you would be at least 50' away if you had to set it from the end in the hole.
Like you said, it would take perfect conditions to make it work.