How much volume is lost after compacting 3/4" crushed stone?
75% sounds like the upper end, I don't really know. I will suggest using sand, 1/4" minus or fines, shown as the 1" of sand in the picture. The 3/4s is for drainage, 1/4 or sand is so you can set them properly allowing for deviation of materials. Delivery is expensive, buy a little extra. Or build back up what you've lost by adding the sand ...