My setup is identical to his. I am running 4.7.5. I am using TakeDamage in C++ as well. Characters take full damage no matter the area that you are within the blast radius.
Are you suggesting that the calculation for the falloff damage is done within the radial damage event vs actually calculating that in the ApplyRadialDamageWithFalloff function? That would make sense as it is always passing the maximum damage instead of lowering it. It doesn’t seem logical to let the TakeDamage function calculate the radial falloff though.