I think the enemies near the start of Snakemolt have a large radius they can move in.

I've seen the Eft go as far as from right up to the room with the Malboros all the way to the entrance of Snakemolt. It seems to me that the pigs, the eft and the drakes can all move about that area as they wish so the assortment of enemies you get at the start my vary.
I could be wrong on this but I know at the very least that the pigs can go all the way to the start (to where you change servers) and the eft can go almost that far, maybe like 3 steps in on Chocobo after server transition is as far as I have seen it go.
I know the Drake can come as far as the first little archway/tunnel you see upon getting into Snakemolt (all of this assumes you're entering Snakemolt at the north end, closest to Traquil and Queen Bolete)