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You actually answered your own question.

A flt is declared payload optimized when any limit weight is projected to be within 1,000# of the limit at pushback. At payload optimized declaration, N/Rs are inhibited and as pushback time approaches, ACS loads the jet with remaining REVENUE cargo to get as close to the limit as possible without exceeding it. If there is too much cargo, they select which boxes and/or pallets to load to sharpshoot the process.

Paid cargo and P/S passes generate revenue and will be used to go right up to the limit. N/Rs, not so much.

(This is different than moving N/Rs for CG, a popular topic of late)

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