YOU are responsible for the code submitted to IB via the API, not IB.
IB has institutions, family funds, and retail traders all trading the API, for years. What do you suppose would happen to that customer base, were a costing fault as you describe, to be found out? (Let's say, via the *annual* trade audits that are performed to demonstrate IB's Smart Routing price improvement performance over that year. Annual. Trade. Audits.) You are saying that you are smarter than alllllllllll these other traders, than federal regulators, than professional DMA auditors. For years.
I am skeptical.
If you have such an issue, it will be found in your code. Your. Code.