As of Columbus3, currency swaps incur the following fees:
 TerraLuna & LunaTerra swaps pay a constant product fee, which increases to disadvantage the more popular of the two trade directions (read Oracle Revamp Proposal for Columbus3)

TerraTerra swaps pay a
tobintax
, currently 25 bp
While the flat tobin tax was designed to simplify the mechanism, recent volatility in fx markets has called for a more robust solution. More robustness could simply be achieved by removing the flat tobin tax from TerraTerra swaps and enforcing the moving constant product fee model to all swaps on Terra currency markets. On an implementation level:
 There exists four key parameters on the market module:

BasePool
: Terra liquidity pool(usdr unit) made available per some small slice of time 
Minspread
: Minimum swap spread the protocol charges for swaps involving Luna 
TobinTax
: flat swap fee for Terra to Terra swaps 
IlliquidTobinTaxList
: exceptionally high tobin taxes

 Let’s do away with the above 4 params. For each of the whitelisted currencies in the
oracle
module, we create a uniqueBasePool
andMinspread
such that the system stores a unique swap constant product for each pair in the set {Luna, KRT, UST, MNT, SDT …}