Functional Coverage at SOC or Sub System Level

Hi All,

At subsystem or SOC verification level,

let’s say there are three IPs integrated : IP1, IP2 and IP3.

Individually from block level verification, all IPs functional coverage is achieved 100%.
IP1 FC 100%
IP2 FC 100%
IP3 FC 100%

But at the subsystem level, when I run some tests or regression, functional coverage is still 60 to 70%. What would be the understanding here?

case_1 : We need to still add tests to make 100% coverage even at SOC level
case_2 : Getting coverage (code or FC) 70% at SOC level is still acceptable, no need to wait for 100% coverage since individually all IPs are already verified.

So, Now I need to sign-off. Can I proceed with just 70% coverage at SOC level,
requesting everyone to share thoughts here.
I am interesting in measuring sign off factors at SOC or sub system level.

Kindly provide your inputs.