Try different TX power to see what works best: 28mW, 42mW, 56mW, 70mW, 84mW. You really shouldn't go higher than 84mW unless you know what you're doing as it could overheat and shorten the life of the unit. If there is no noticeable difference between those power settings, set it to 42mW and leave it.
Also be sure you're set to 40MHz Channel Width.
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