I'm not sure you guys are understanding how start bias works...
Austria - Hills
Brazil - Jungle
Mongol - Plains
Morocco - Desert
Poland - Plains
Sweden - Tundra
Venice - Ocean (Always)
Byzantium - Ocean
Indonesia - Ocean
Korea - Ocean
Portugal - Ocean
Carthage - Ocean
Spain - Ocean
Celts - Forest
Netherlands - Grass
England - Ocean
Ottoman - Ocean
Arabia - Desert
Aztec - Jungle
India - Grassland
Iroquois - Forest
Russia - Tundra
Inca - Hill
Polynesia - Ocean
Denmark - Ocean
Egypt - Avoid Jungle, Forest
Siam - Avoid Forest
Songhai - Avoid Tundra
Assyria - Avoid Tundra
Babylon - Avoid Tundra
Huns - Avoid Forest, Jungle
Zulu - Avoid Jungle
I may be missing some newer civs here.
Certain civs have "first pick" when it comes to start bias, like Venice. I think you may be attributing start biases to civs that don't have them. Start bias can be tricky to weigh because of where it ends up landing you. For example, it would appear the Dutch have some sort of desert bias but they have a marsh/floodplains bias that often lands them near desert. You also need to take into account the various other factors to a start bias, again for example, tundra starts tend to have much more defensible capitals due to being on the edge of a continent. There are loads of "hidden" advantages like this for each civ.
Anyway, there's no such thing as a "one-tile island" start bias or a "trapped/isolated" start bias.