Cura Parameter Confusion: Initial Layer Flow Rate
If you're over- or under-extruding by a 30% margin, there is going to be so much excess or deficiency of material in the first layer that it will take a few layers to "catch up". Normally you would only adjust the flow by 5% or at most 10% unless you're using it to correct for compression of the filament in the extruder gear (for flexible filaments), but adjusting first layer flow only is always a hack to work around incorrect bed height or adhesion problems. You'd do much better to figure out the right solution to whatever problem you're trying to solve with flow.