I'm doing some construct building for an NPC and note that it's more costly for the construct to be a Large creature than to have two levels taken off the crits. Given that constructs are immune to stun and bleeding, it seems like it would be better to have crits two levels lower than Large crits, as the Large ones deal more hits. There is the issue of penalties and "you're dead" results, but overall, it seems that it's better to be two levels lower on crits than Large if you're immune to stun and bleeding.
Am I missing something?