iOS and fog

I’m trying to port an Android game of mine. Basically my playing field is a long board that the player cross from one end to the other. On Android I’ve added a fog effect so that it seems like the end you’re going towards is coming out of nothing. I’m using linear fog because exponential doesn’t work on Android, it makes my whole scene goes gradually white (the color of the fog).
Strangely enough the same thing happens in iOS but if I use linear fog. The other two exponential kinds also don’t work and completely mess up my perspective (even making some objects disappear).
Any ideas on how I should implement this fog effect on iOS?

Did you find a solution to your problem? Seems like I have the same issue.