You don't want that extra layer for IPS separate from the rest of the Threat Prevention policy. This special "IPS" layer is only intended to be used for pre-R80 gateways, and reflects the fact that IPS was separately configured from the Threat Prevention policy on R77.30 and earlier gateways. Its presence does not dictate the priority of enforcement making IPS first, only that there is at least one pre-R80 gateway using IPS in your configuration. Once the last pre-R80 gateway using IPS disappears from your configuration the IPS layer disappears as well.
It is much easier to have IPS integrated with the rest of the Threat Prevention policy on R80.10+ gateways.
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