You don't need a 1:1 ratio to fly off grass, it all accords how light you can build, get the weight of your chosen airframe close to your available thrust and you can fly off anything, I had a fully loaded (brakes, air up down retracts, trainling link UC etc) Elan with a P80 in it and it flew off a grass sheep field without any problems, take offs in less than 50ft, that was a 23Lb airframe with a 19Lb turbine, I used to hold the Elan on the brakes and push the throttle to full power, when it started to slide forward, release the brakes and off she went.

What has to be learnt is how to land a heavy loaded airframe sweetly and on the spot, to many of the vidio's you see show the turbine flying past the pilot before it lands, to me it should land in the same position it started its take off run, in full size landing on the numbers was a great achievement.

Mike