F marked FSB remedy on AR15 Rifle build

Built a 20" A2 rifle (Retro Integral Carry handle upper ) and CMMG only offered F marked front sight blocks not standard A1/A2 Rifle front sight blocks . To remedy the difference in height between the two FSB is there a changeup of the front sight posts ? one can be longer or shorter to offset the minor but affecting difference ??

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F marked FSB remedy on AR15 Rifle build