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While I think ISynchronizedObjectInstanceCache is generally a better idea, I don't think using that will help with reducing the amount of request. ISynchronizedObjectInstanceCache ensures that the cache invalidation is synced, so each instance still has it own cache, and adding an item in an instance will not make that cache entry available on all instances
"StaticallyCacheFor" in Episerver Find uses the "HttpRuntime.Cache". Using the "SynchronizedObjectInstanceCache" instead would reduce the amount of requests to Episerver Find when running a lot of instances.