Remote Area by Coverage Along Floor or Slope?

I am working on a project with an attic. The pitch of the attic is 12:12 and the structure is combustible construction. The area is being used as a mechanical room so the fire sprinkler layout will be Ordinary Hazard Group 1 and a wet system will protect the space since the temperature will be maintained above 40ºF. Standard spray sprinklers are being utilized because Attic sprinklers are only listed for Light Hazard use.

Using a quick response area reduction, the remote area will be 1,500ft² (OH1) x 1.3 (30% pitch increase) x 0.6 (40% quick response decrease) = 1,170ft².

Since the sprinklers are spaced along the 12:12 pitch, the floor area in plan view is substantially less than the square footage being protected along this steep slope which picks up a ton of sprinklers when I draw my remote area based on the floor. I can't find any guidance in NFPA 13 about remote area on a slope besides the typical 1.2 x √RA split between sprinklers.

Should the 1,170ft² remote area be measured based on the coverage of the sprinkler along the slope (as the protection is spaced) or should the remote area be based on the floor even though it picks up way more sprinklers than 1,170ft² of actual coverage based on the slope?

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