What is the proper harness strap height for rear-facing installation?

For rear-facing use, harness straps should be at or just below the child's shoulders, and the top of the child's head must be at least 1 inch (2.5 cm) below the headrest adjustment lever. You should adjust the harness height by squeezing the adjustment handle and moving the headrest to the proper position.

From the official Graco 3- 1 Car Seat manual, page 13

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