https://dev.banana-pi.org.cn/Image/BPI-R2/Openwrt/1806/mtk-bpi-r2-SD.img

Is there any description how the file above was created. All install-images on OpenWRT website have approx. 4.5 MB and do not boot the BPI-R2 when written to SD. That above image boots a BPI-R2 and is approx. 71 MB . If there is a description it can possibly be adapted for the new 19.07 version of OpenWRT