You and the other poster have it. Without seeing real data on that challenge coin,well the idea is interesting but I'd like to see real world results.
You can use FP's as is in a:
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Where == is the barrel, your end cap, blast camber space, stacked freeze plugs, end cap.
You will/should need a blast chamber of between 1.25 and 1.75 inches, jury is out IMO on where the best length is because legally you cannot change the count of plugs, nor can you have extra baffles that changing the configuration would cause. I go with just enough blast chamber to clear my muzzle brakes, I use Griffin Armanent taper mounts on most of my F1's.
Your freeze plugs will work better if you put a cone in them. You can get dies for this on Ebay for around $90-$100 or you can pick up a set of sloped torx bits like they show in SDTA, or you use a lathe center bit. The plugs will work in a flat shape but you'll be happier if yo ucone them. The whole thing is you want to keep the gas in the tube for the longest amount of time and having the gas go through a /\ shape pointy end first means some of it bleeds off into the space, then has to backtrack a longer distance before it can go forward again.
You'll have to wade through the two ginormous threads on F1's the $100 and $250 ones but you can get a lot of information there along with hearing how people would change the way they did things.
Me I tried various methods of making cones and in the end picked up one of the ebay dies. They may not be quite as deep as ones I can do with torx bits and or various cone shapes but they're always centered and they never split and tear which I had a fair problem with with other methods. And when I get my current open F1's done I'll sell it on the EE with some expectation of getting back a fair chunk of what I put into it.