ORIGINAL: Froonp
Yes, That's what I though too, the correct terrain hexside should be a river.
But, Singapore is so small (See this extra map from the Wikipedia) that it doesn't even warrant a full hex (Pacific scale I mean), so the depiction made on the WiF FE maps is correct at the Pacific scale.
So from a game point of view I think that Singapore should be treated similary in both MWiF & WiF FE, and so should be attackable from 2 hexsides, fortified on the 4 other hexsides, and be constituated with a jungle terrain. It should be drawn as an island contained in the same hex than the malayan land on the other side of the Tebrau Straits.
The fact that the neighboring hexes are not exactly the same terrain is less important to me. With the scale changing, it can't always be the same as WiF FE.
Ok. So how about all three hexes being jungle (Singapore and the two hexes to its north) with no intervening hexside terrain. The other 4 hexsides would be the same as in CWIF: fortified with all sea hexsides connecting to a couple of island hexes and one connecting to Sumatra?