What is melee combat?

What counts as melee combat? Because outnumbering says its Melee combat exclusively. Yet if I have a 1" threat range and my second rank models cant reach, are they in range? Because the rule for moving in melee say yes, but thats to move into engage. Situation was this. I had 8 models in two ranks against one huge model. Due to heavy rains I could only move 2" to get into engaged and could not get there. Does that mean for outnumbering 8-1 I count the whole squad or only those within their threat range? We have a playing building a rat slave horde if it counts the whole squad...woo boy nobody is beating him on enhancements. Bonus question: What is the LoS from a flying model? It does not say but its 9" above the battlefield so I'm guess its a 9" diagonal downwards but it does not say.