I know from your HDYGO posts that you're a born-again roach angler (no offence to carp anglers, Christians or anyone else) so I'm wondering what you want your groundbait to do. Are you wanting a cloud to colour clear water because the fish or so spooky? Or draw fish up in deep water because it's easier to catch them there? Or something else? I'm no expert with big roach, but when I'm after decent roach (my idea of decent roach, fish of 12oz to 1lb might fall short of yours) in deep water, it's often a case of using a heavy'ish groundbait to bring some fish, of any size, into the swim, and then feeding eg seed baits like hemp and tares and trying different depths, to try and encourage and pick out some of the bigger ones that eventually come in.