While Wheeler has the lowest fail rate for low leverage situations, his FIP does measure higher. His relative FIP is much better however. Due to his penchant for HRs he will never be a qualifier for an extremely low FIP, but that does not account for frequency. Given his low failure frequency, the lesser magnitude of a home run in low leverage spots, and his relatively strong FIP, it is pretty clear where Wheeler's use is best suited. Likewise, there should be no further questions about Balfour, unless you want to discuss his health.