https://bitsharestalk.org/index.php/topic,17165.msg219360.html#msg219360 BM answered here

I think they need to be high enough such that when converted to BTS at the "fee pool price ratio" they meet the transaction fee requirements. I believe issuers of UIAs and privatized BitAssets get to set the "fee pool price ratio" to whatever they want (although I assume they would set it to the market exchange rate between the asset and BTS). As for network BitAssets, according to this it seems like it is determined from the price feeds directly.

I appreciate any clarification from the devs if I got any of this wrong.

Can anyone point a source? Is it $0.2 the same as BTS?