If your sump is setup so that the drain portion is compartmentalized, that portions' level will never change regardless of the topoff level. You can even use a bucket or a large piece of pipe as long as its higher than the rest of the sumps water level.
That said, your PINK
baffle (which is very, umm, "sensitive", BTW
) WILL quiet your flow a bit. This is used in the HOB Deltec skimmer to quiet the flow.
HTH