This is more of a General Product Topics question.
You won't necessarily see drops in SmartLog when traffic is limited.
From the notes I've seen internally, this is what you should be looking at to validate that limiting is happening (granted, this is from R75.40:
fw ctl zdebug -m APPI all > dbg.txt
In dbg.txt, look for: fw_appi_limit_set_matched_data: Set new rule_id: (rule_num)
This will tell you that traffic is being matched to a rule with limit.
Note this debug can be overwhelming on gateways with a lot of traffic, so I would only run it fairly briefly.