You stated that your Commitment - $0.424/hour
Hence if you run your 6 servers for 24 hours per day over the course of 1 month and wish to use SP to cover all the running hours (i.e. 100% coverage) You will need to purchase $0.074 (SP Rate) X 6 = $0.444/hour as a commitment to attain 100% on the savings plan.
What you see currently covered by EC2 Instance Savings Plans: 4393.599 Hrs was due to the purchased SP commitment/hour which didn't cover the entire 4,464 hours in that month hence the rest of the hours not covered by the SP (~70.4 running hours of the 6 instances) will be charged at On-Demand rate of $0.125/Hr.
Hope the above helps!
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