Deliver a Ruleset stack that positions all Pega Rulesets below the Rulesets introduced for the Client applications, including its Enterprise layer. Pega-provided Applications are not tested with non-Pega Rulesets in between them and the Platform Rulesets, so you risk unexpected behavior if you deliver such a Ruleset stack.
Pega Applications do Ruleset-specialize rules from Pega Platform, which would override any Ruleset-specializations you introduce in the Enterprise Layer if the Pega Application Rulesets are higher than your Enterprise Layer Rulesets. Of course, this would not be an issue if you Class-specialize in your Enterprise layer, but this isn't always possible.
Consider having a Ruleset in your Enterprise Layer dedicated to any Ruleset-specializations required of Pega-provided rules. If you have one or more Pega Applications, scale this out to a specialization Ruleset for each Pega Application, following the same order as the Applications on the stack.