Home Improvement → [HVAC] Clearance for exhaust vent from new furnace

A new furnace had been installed, then a water heater was installed.

To accommodate water heater vent, had to raise connection at
furnace which raised common double wall exhaust pipe above roof

Question: how much clearance is need at that point above roof line inside the roof cap? Currently there is about almost 2 inches and this certainly must be wrong. How much should there be?

Thanking you for your comments in advance

Nanco

Refer to Venting Tables