In this paper, we report on the increase of exchange bias in Ir/Mn exchange biased systems due to an increase in the setting field. This is related to the size of interfacial spin clusters. Six samples of Si(100)/Ta(5 nm)/ Ru(5 nm)/IrMn(10 nm)/ CoFe(3 nm)/Ta(5 nm) of varying grain size were prepared by direct current (dc) sputtering. Magnetic measurements with increasing setting fields were taken along with grain size distribution measurements from TEM images. After the setting field had increased beyond the saturation magnetization of the ferromagnetic layer a continual increase in exchange bias was seen. This increase varied according to the size of the interfacial spin clusters.