Minneapolis Fire is essentially only on site 1-9 (almost all structure fires are patched with an ME-Tac; you will be able to hear them elsewhere). Trying anywhere else is not going to work.
Moving your antenna (inches or to the other side of the house) can make a huge difference. I* am in the white or yellow on that map linked above and am currently decoding ~100% of control channel messages and have a BER < 0.1%. I could move my antenna a few feet and have it be completely unusable. You should select only site 1-9 on your scanner (listen to everything on the site) and see where you are able to get it clearly and where you can't.
* I am using a somewhat directional antenna, the antenna is in front of a window and I am not using a typical scanner, but I think the basic point still applies.