I don't believe there's any advantage that trimming the nozzle flush inside. There is not an inside groove for the fillet to cover as shown in Detail 5.
The nozzle extending inside provides more metal in the reinforcement area making this a stronger design.
ASME VIII Division 2. Table 4.2.10
Can a nozzle be calculated a flush nozzle and actually be fabricated with an inside projection without the inside fillet?
Are all nozzles without the inside fillet required to trim or set flush inside?
Detail 3 vs Detail 5
Thanks
RCD