For whatever it's worth, a change in flavor is a natural property of rayon wicks. Fans of rayon attribute the different flavor to not tasting the cotton, those (like myself) who don't dig rayon will tell you it mutes the flavor as opposed to cotton. It's all a matter of opinion, there's no real right or wrong, but that could explain you not getting the flavor that you're expecting.
What's not a matter of opinion is that Rayon works differently than cotton. If you imagine spilling water on a counter, then laying a paper towel over the spill. Initially the towel will be wet where the water spot is, but the water will quickly spread throughout the towel as it absorbs the water. Eventually, the whole towel will be wet as it absorbs. This is more or less how your cotton wicks work.
Rayon. on the other hand, works more like laying a hand towel on the water. It will absorb the water in spots but be dry in others. Unless, of course, there is enough water to wet the whole towel. So basically, you need to plan your rayon like a channel. You basically want it to leak at the bottom and dam up under the coil. It's more like directing juice to the coils instead of spreading it to them.
Undoubtedly, rayon is tougher to work with. Arguably, it's an inferior materiel. Can you name a coil manufacturer that uses rayon as opposed to organic cotton in their coils? There's a reason why most, if not all, use cotton.
My suggestion would be to wick the tank with cotton. Once you have it working right and you know how it should perform, you can give the rayon a try again. It will be easier to figure out once you have mastered the cotton, and it will allow you to compare and contrast the two to see which you prefer.
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