Can you guys help me with this loft/sweep issue?

hi guys,

i've attached this flange model where i have a solid flat surface  and rounded cynlindrical surface above I want to be able to loft or sweep a profile or even extrude boss (up to next, but when I do this the solid flat surface extrudes all the way through cylinder and not just molding with it) can you guys please advise on how I can pull this off?

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