I'm pretty sure the problem for your scanner is signal strength, and / or system signal timing , but it's worth experimenting with the scanner's attenuation setting since you've tried everything else. You could also try a Yagi antenna like this:
https://www.amazon.com/gp/product/B00EC804SO/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
and point it in the direction of the nearest system tower to your town (Sunderland?). The Yagi is a directional antenna, and is sensitive to signal sources it points towards, and rejects signals it is not pointed at, if that makes sense.
I don't think I can *solve* your reception problems, but I can verify a signal quality issue. I need to resolve an equipment issue, and a south county / Calvert trip might provide some useful data. I can probably start to receive Calvert in Tracys Landing / Deale, but if I have the time I'll roll into North Beach.