Oh bummer! So close! I agree with you. From everything I've read, you catch little swarms in small traps and big swarms in big traps. HB Democracy says 40 liter volume is optimal.
PS. You watched them for 48 hours? Didn't you put 2+2 together and think, wait, that swarm is huge, they are not going to fit into my little nucs? lol Oh well, don't take that the wrong way. You live and you learn.