51.1%
A husband and wife near age 50 with W-2 wages at the max ($285K in 2021) have 7 employees from age 25 to 57 with wages from $10K to $51K. The owners are able to contribute $337K for their own benefits, supported by $17K for employee benefits--thus garnering 95.3% of their $354K total cost. (Their personal 401k maximum deferrals for the year are included in these numbers.)
The table below is based on:
The contribution amounts are additive for a 2-person plan.