I need to have an outer glow on the entire coastline of my map. The way QGIS creates glow effects with a gradient from alpha=1 to alpha=0 creates a problem, that whenever the glow overlaps with itself because of the geometry of a shape (e.g. bays or islands near the coast), it will reinforce its own strength at the overlapping location (see image). This creates an uneven distribution of the glow effect.
I noticed that there are a bunch of different blend modes for the outer glow effect, yet none of them seem to prohibit this kind of self-reinforcement.
How do I resolve this issue?