You will find that typically this time of year the fishing dies down everywhere. The reason for this is the fish's metabolism also slows this time of year. They do not have to eat as much to get through the day. For this reason, they are also less likely to travel very far for a meal, so you must place the fly on their nose.
Regarding your question about streamers and midges. I always tie my streamers with a conehead and wrap the shank with lead wire so it sinks quickly. Does it make a difference? I don't know, it is just personal preference. When fishing a midge in a deep hole, you have to realize that if the hole is 3' deep that putting your indicator 3' up from the fly will not get it to the bottom. The reason is that underwater currents and drag on the fly line will cause the line to take a sagging appearance. So, you may only be fishing 2' deep, but you believe you are deeper. The best way to get deeper is to add more weight by either adding split shot, or my favorite is to add another nymph 12" below the first. This not only doubles your chances at a hookup and allows you to work more of the water column, but also gives additional weight to reduce the sag in your line and have a more vertical presentation.
From my experience when fishing a hole that is around 4' deep, I would put my indicator about 6' above my bottom midge if using 2 size 20 bh zebra midges. A technique and setup I commonly use on the Clinch.
Hope this helps.