Couple things about this -- first, recent Swarm changes mean that 2x2s should be able to swarm, the summon will just appear in some adjacent spaces; second, Melt Down should not be triggering Bestow, because Melt Down is listed as a Sacrifice effect, and those prevent on-death triggers. If you use Melt Down to trigger any on-death effects, then that is bug abuse.
I know this is an old thread, but I just want to say you can totally swarm with 2x2's, even prior to any recent changes. You just need to ensure the 1x1 you're looking to swarm has clear spaces as though it were the top corner of a 2x2. I used to swarm with Vindrax and Valdac beck before Mimic got changed.
It was changed after that , wouldn't work even when spaces were clear. On the topic it's kind of useless now in Constructs since Swarm changes, I wanted to use this before to swarm Rugolths Revenges
Heros shouldn't have been able to swarm in the first place so they patched in the 2x2 fix as well in the process.
Well I just checked and "Swarm" is replaced by "Swarm: Clockwork Swarm" so you regardless of what unit it ends up on, it would always spawn a Clockwork Swarm with no upgrades. Split might still be interesting but doesn't feel as easy to abuse (will have to play around with it).