This works for me: Bake @ 325 degrees and when cake is done remove from oven and lay a dry dish cloth on top. Press gently all over top until the cake is level. Let rest a few minutes and then remove from cake pan onto cooling rack. Be careful it will be hot with steam while you are pressing.
I have always used mixes, If you add 1 extra egg plus 1 dry instant pudding, to each cake mix you will find a world of difference. Also, are you baking at 325 degrees? I use Duncan or Pillsbury, according to the flavor I am looking for. Been doing this for over 6 years, works everytime.
I like the texture of my Smashed cakes too. You don't have to chase the cake crumb all over the plate. If you bake at 325 degrees your cakes bake longer but do not rise as high in the middle. As for the cake strips around the pan, I use the nail in the middle of large pans and that works just fine.Just my two cents.