When you blend two volumes in Max mode, subtract your previous volume to the one you’ve just combined. it isolates the upper part of the volume you Max blended. now clamp it with a Histo scan and add an edge detect to select the outline. blur that selection and you now have the Mask of the intersection of your two volumes. go back on the blend Max step, blur it slightly and blend it with itself according to the Mask you’ve just created. that way you can smooth the intersection of two separate elements and have something that feels less artificial.