I also had a problem with them when I lived in the city. They would line up on the roof of my house and then come down and fill up. They would hog the feeder by sitting in it, just sitting right down and making themselves comfortable. I had a platform feeder made out of an old window screen. I would run outside waving my arms and yelling but they wouldn't go far.

I had to get rid of the platform feeder and started using feeders with no seed catcher. I think they were really attracted to corn the most. Looks like they like your safflower very much.

Iam thinking of putting my safflower in a tube feeder don't know if the cardenal would eat from there
Anna

The cardinals will probably eat what falls to the ground, which will be a lot. The male and female ones at my house both eat on the ground. I only had to make sure the feeders were far enough from the bushes so that a cat couldn't hide and jump out at them. I lost my catbird that way. So I moved the feeders and put up a short fence at the edge of the bushes. The cat will have to squeeze through the fence, which I hope will give the birds a chance to get away. So far, so good.