Well yes, but the fact that you've killed no monsters means you still have a ton of full heals. Also, any extra conversions you get are an extra full heal. You really aren't missing that much bonus. Goblins don't get very good stats for bonus kills.
The more the discussion goes on, the more I think that the principle of stacking XP is fine. It would offer some powerful combinations, but that's what we should expect from a racial bonus. Maybe 5 stacking for 100 conversion points is a bit high. Maybe it should be 4 stacking for 100 or 3 stacking for 85. However, I think that this is the direction to go.