This is because more often then not, the lower arc results in missing the LOS targets that default higher arc LOS LRMs would have hit.
In fact the only case where low arc missiles don't consistently miss a lot more then the high arc missiles, is when there is a low ceiling blocking all high arc missiles... which is almost never the case.
And has nothing to do with being in LOS or not : It's all about being under a ceiling or not.
Edited by Humble Dexter, 24 March 2019 - 06:13 AM.