How to reduce index size

How to reduce index size

We have an ELA build 8000. Index drive is 450 gb and it is mostly full. We don't have a lot of servers on it about 100 or so. And under F:\Archives\Indexes\2\univindexes\cold folder I see archives which is  6 month old, although our " Retain Archive Logs" interval is setup to 1 month and " Compress Index files older" than and " Compress Universal Index files older than" both setup to 3 days. 

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