It is great that you are using ZL18. I found that doing Helicopter flight over the Balearic Islands, the high resolution did enhance the experience a lot.
ZL18 is a great choice.
(Would be awesome if we had True Earth Taiwan in ZL18 for X-Plane someday. It is 36.193 km² but the True Earth Washington release had 237,956 km² in ZL17. So True Earth Taiwan in ZL18 would require less disk space than True Earth Washington in ZL17.)