One thing that I have found is that the landscape is very LARGE with ATG and it is easier to think there is a lot more ocean and islands than usual. But maybe it is really not that much different than usual since biome zones and mountains etc. are simply so huge.
You can get unlucky and spawn in "ocean" world region. That happens with vanilla/BoP world gen too. And in my experience you ALWAYS spawn on a beach somewhere. I usually "cheat" a little and use creative flight to find myself a good place to settle down. Actually I use creative flight to test out seeds before I pick them. And I go through a LOT before I settle on one.
Lastly I know that Eyamaz did a lot of modifications to the ATG configs for 1.6 modpacks and they were distributed to all packs through universal configs. Not sure if this is the case with 1.7, but probably not. I also think ATG have shifted authors/developers since then, so things might have changed. But it have never been unusual to get lots of tall mountain "fingers" in ocean biomes.
Oh and if you are curious, this is a map of my ATG+BoP+Highlands world for 1.6.4 using Eyemaz's configs: