A bit of a belated reply to your post, almost 24 hours in fact!
My birds use the cage guardian all the time, after they had got used to it. I use the sort with a mesh to allow Blackbirds and Thrushes, so I get all sorts in there too. It's placed under the branches of bushes at the foot of a big conifer, where I have created a woodland style environment. (It makes my garden sound huge, but this area is only about 10 sq.yards or so.) I put the guardian there to protect them from any cats which might creep up, and the Sparrowhawk. That area and the cage provided a refuge for moulting Blackbirds, and it's where the Song Thrush first appeared, and where the male Blackcap first appeared. I have a slab of tree trunk as a 'platter' on which I put ground feed. This is a mixture of insectivorous foods and pinhead oatmeal, with sultanas by the side. I hoped this would attract the ground feeding birds, and it has. The Blackbirds are waiting every morning for me to replenish the 'platter' if I'm a bit late, then the Thrush, Robin, Dunnocks and Chaffinches turn up throughout the day, plus Starlings and the Squirrel sometimes.
I can't imagine that you are doing anything wrong. Birds are funny sometimes. so I don't really know what to suggest.
I have only been doing serious bird feeding for about 18 months now, and am constantly amazed and delighted by what turns up in my garden; birds I'd never seen in my entire life, and birds like the Blackcap that I'd never even heard of.
Hope this helps for now, and keep in touch with what happens in your garden.
Good luck Silver, and again it's Goodnight from me!