I answered this for you but ... an all mighty moderator deleted all my posts yesterday because I was giving some SEOs shit for using GSA like noobs.
So here is the answer.
First off where are you getting your LSI?
If you're scanning pages/keywords that have things like Wikipedia or Amazon or big hit DA sites you may be using LSI that doesn't really matter. So only scan LSI from relevant sites that are fighting for these spots (and not Wikipedia they're the huge 10,000 pound gorilla that gets into any party because... they're a 10,000 pound gorilla, Google is not gonna say no to their invite).
THEN... sorry to say the best way to go about this is either
A. Use a software called CORA because each keyword is different!
or
B. Find out the main keyword/LSI you want to use and go through these sites manually and count
Cora is expensive and is a pain in the ass to learn, but will make a huge difference for onpage.
Best of luck