Tracking OI on options is a better idea than futures.
The idea is that option writers are the smarter lot. People who write options are putting up more money vs the one who buys. So this entire OI logic is saying be on the side of the option writer. So if OI on calls is going up, means option writers are coming in to write calls, so expect markets to not go up.
When it comes to futures, when price goes up with reduction in OI, this means that existing shorts are in a hurry to cover their losses. Which could be the possible reason why price is going up. Whenever the short covering ends, it may stop. But when market goes up with OI increase, this means this up move is not because of short covering. So this could possibly continue to move up for longer.
But yeah, all of this doesn’t really make sense all the time