The target AFR is only supposed to be a guideline. It tells the ecu about where you want the AFR to be so it should be set around 12.5-12.8 and leaner down low near idle midrange. You change the MAF tables to tweak how the engine runs or the VE tables which it doesn't look like you have access to. Target AFR is there to tell the ecu when to start correcting itself. You need to change the air flow tables to make the ecu run right in the first place in order to give you the afr values you want. Both tables need to be changed in order to work together but the Target AFR table shouldn't have to be changed that much maybe a few points here and there.
Basic guide to nissan tunning
http://www.plmsdevelopments.com/file...ing_basics.pdf