i agree, from my experience you can get 7kg in the 20L and get into the 1.070's pretty easily, even with a 60 minute boil, if you are a bit careful with the mash. that said, i am not at all against using a bit of DME to boost gravity a bit or fine tune a batch, it's a useful tool in the toolbox, i get upset when people berate its use! but i wouldn't be afraid to go higher on the base malt and cut down the dme if i were you; 6kg is easy to mash (your 11 lbs grain bill = 5 kg). i have had a couple batches with >7kg grain bills get a bit stuck so i am a little cautious now when i load it up, but i have been having great results lately, with efficiency around 73-75%. i now always open the machine and stir the mash a few times at pump breaks, and sometimes can see that it's getting a bit glumpy or starting to channel, especially when i use a lot of wheat or oats. don't be afraid of a longer mash, i sometimes do a 90 minute rest at sacc temp, and i generally don't add specialty grains until the end of the mash (15-20 minutes left at sacc temp), save the space at the beginning for stuff that needs to be mashed. check the temp at the top of the malt tube often, especially just after temp changes, to make sure there is good flow through the grain; if the wort isn't circulating well you will have warmer wort outside the tube and cooler wort inside, of course a few degrees difference is expected, but if this happens it's time to give it a good stir.