This is a guide to improve the decal placement for melee weapons. I have a guide on adding new surface decals and emitters here:
https://defusestudios.com/sgk-adding-surface-emitters-and-decals/

Go to the BP_MasterWeapon bp then select the Multicast Spawn Hit Emitter event and add 2 new vector inputs, first one named Decal Start and the second Decal Direction, Then create 2 new vector variables named them same and set the using the inputs of the event.

It should look like the image below.

Next create a new variable called Decal Hit Result and set its type to Hit Result. then create another variable and call it Melee variable type bool.

Now select the Multicast Spawn Hit Emitter event and add another new input variable type bool and called it Melee now copy the image below.

Next delete the highlighted nodes shown in the image below.

Next create a custom event called range decal then copy the image below.

Next create a new custom event called Melee Decal and copy the image below.

Next copy the image below.

Next go to the BP_MasterMeleeWeapon then go to the Give Damage Once then go to each of the Multicast Spawn Hit Emitter (There are 3 in that function) and copy the image below for each one of the events.