Now if you need to optimize your hashrate of your LHR GPU (75%), Follow the following steps :
1 Download NBminer v 39.7 from this link on github .
2 Go to Nicehash > Plugins > NBminer .
3 Click to the three dots, chose "Show internals" .
4 Select bins floder
5 Rename 16.4 folder to 16.4old
6 Create new folder 16.4
7 Extract the NBminer 39.7 plugin that we was downloaded on the new 16.4 folder.
8 Re-benchmark (Benchmark tab > NBminer chose your algorithm (Ethash)
Enjoy with 75% LHR unlock