I live in a concrete building, on the fifth floor, in Boston's South end neighborhood. When I first I moved in, I was using my old rabbit ears on the TV in my living room. By aiming them directly toward the window, I could pick up channels 2, 4, 5, 7, 25, 38, 44, 56, 62, 66 and 68 perfectly. In my bedroom, I had a single rabbit ear antenna on an old TV/VCR combo. I could pick up all the same channels except no 66, and 38 was marginal at best.
I purchased an Amazon Basics amplified 50 mile range flat antenna for about $25. I removed the amplifier and do not use it. I find that hanging it in the window works fine to receive all my locals, but it is far from being the optimal position to receive the most channels. Laying it horizontally flat on shelves to either side of the window is the optimal position for me. I am able to receive all the aforementioned channels perfectly. I also can now pick up 8 WBTS-LD Boston, 10 WJAR Providence, 24 WFXZ-CD Boston (prior to channel-sharing with WGBH-TV), 27 WUTF-TV Worcester, 48 WYDN Worcester, and 58 WCEA-LD Boston. So the newer antenna did work much better for me.
I also get weak, unwatchable signals on 6 WLNE-TV New Bedford, 12 WPRI-TV Providence, 13 WYCN-CD Nashua, 28 WLWC New Bedford (prior to channel-sharing with WPXQ-TV), 46 WWDP Norwell, and 60 WNEU Merrimack.