Possible Clues:

• A single M in us?
• Singularly like 16 down
• Almost as many
• Almost equal to, with 'than'
• Not quite as many
• 1970 hit, "___ Bell To Answer"
• M in us on E?
• 1 and 26 down
• One M in us?
• That could make sons around 20 down but not quite so much