Standard horizontal sidewall sprinklers shall be located ______ to 6 inches below the deck.

The correct answer states that standard horizontal sidewall sprinklers must be located 4 inches below the deck. This requirement is based on the guidelines that help ensure effective coverage and distribution of water from the sprinkler during a fire event.

Positioning the sprinklers at this specific height allows for optimal performance by ensuring they can intercept and respond to heat and flames effectively. It also accounts for potential obstructions and the need for proper spacing between sprinklers to maximize their efficiency in providing a uniform spray pattern across the space.

While the other options suggest different distances, they do not comply with the established standards that dictate 4 inches as the appropriate installation height for this type of sprinkler. Adhering to the correct placement is crucial for maintaining the integrity of fire protection systems and ensuring compliance with safety codes.