How does URF's "Heal Embargo" stack with Grievous Wounds?

Is it Additive or Multiplicative? Say a champion heals for 300 and HE (Heal Embargo) is at 50%, so it would be: 300 - 50% (150) = 150 right?

Now lets add GW's (40%), HE is still at 50%. Is it: 300 - (50% + 40%) = 30 or 300 - 50% (150) - 40% (60) = 90 or 300 - (.5 x .4) = 240?

I just feel like some champs heal for way too much with both GW and HE