Actually, at most heights, zoysia is so woody that cutter without a shearing action does not work well. Your next investment needs to be a Maruyama Landscape Blade. So the parts next to the fence and around trees matches the main lawn. String trimming is for weeds, not fine reel mowed turf.
They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin 1775
Sell not virtue to purchase wealth, nor Liberty to purchase power.
Benjamin Franklin Poor Richard's Almanac1738