First, make all income, earned and unearned, subject to Social Security.
Second, remove the cap.
Think if Pro Athletes, movie stars, CEO’s, and others who make large incomes had to pay SS on every penny earned. How much does LeBron James make a year?
I generally have my SS paid up by mid April or May. I am willing to pay the 6.2% all year. Keep a cap on what the employer matches, just have the individuals pay all year.