I've got a determinate - Bella Rosa, and an indeterminate, Bodacious growing in the Earth Boxes at the moment. I lost track of which seedlings were which type, so Bella Rosa has two plants, and Bodacious has 3 in it. Strangely enough, Bodacious has more fruits in it. Of course, as you say they're crammed in there pretty close so I can't tell which plants have which fruits but can tell them apart by the size and shape.
I think cramming 3 indeterminate plants in an Earth Box stunts them a bit, and makes them bear earlier for me. Given our limits on growing season, ending in June or so it makes sense at least if you start late like I did this year. IF I get the seeds started in September like I'm supposed to, I'd definitely only put two plants in each box. I do over-fill the boxes (mound up the soil) and use the plastic covers with the white side up to keep the soil cooler, so it's at least 10gal of soil in those boxes, I think.
Without the cages, the plants do get to be a huge tomato jungle starting in late spring.
