Recent work has developed supine breast imaging for improved correlation with surgery and comfort but will likely require breast-specific coils to maximize the SNR. Comparing prone and supine SNR can be difficult due to substantial deformation between the positions and heterogeneity of the patient population. We measured SNR in a constant-tissue model to reduce dependence on tissue heterogeneity and provide an overall SNR across the volume of interest. We compared SNR of a novel 60-channel supine coil and a standard prone coil. In the cosntant-tissue images, the supine 60-channel coil increased SNR by 33%, 78% and 80% across 3 volunteers.