I'm inspired by your experiment to get back into the world of light clay. I've done some building in light earth and found that not compressing it still produces a very strong wall, but much lighter and with better insulation. Of course there is a sweet spot which will depend on the earth, the type of straw and the insulation/ thermal mass properties desired, but I would suggest doing more experiments to see how loosely you can pack the blocks and how lightly you can coat the straw with clay slip without losing too much strength. I've been thinking of doing these experiments myself after watching a friend make hempcrete blocks.
