I think you've got that backwards Charlie. It's not more Sb than Sn, linotype has 12% Sb and 5% Sn and print shops (when it was still used) used it for years at a time without it becoming "too soft". Also many people use WW alloy at 2% Sb and 0.5% Sn without adding any additional Sn with excellent results whether air cooled, quenched or oven HT. When the Sn is a significantly higher than the percentage of Sb is when the amount of hardening is reduced and the amount of age softening is increased. More tin than antimony also creates "free" tin in the alloy which some believe can lead to leading though I'm not too sure about that. For many decades tin was the hardening agent of choice in Pb/Sn alloys and still is with the front stuffers. When Sb is added to the alloy is when the Sb/Sn is best when balanced, a very common practice in the metals industry.
Rick