We consider the problem of bounding the loss rates of the aggregation of on-off sources in a bufferless model by the loss rates associated with the aggregation of i.i.d. on-off sources. We use well-known results from the theory of variability orderings to establish a conjecture ofRasmussen et. al., a recent upper bound of Mao and Habibi, and to discussa new conjectured upper bound by these authors.