This Community article might help.
I'm also using the Hauwei HG659 in a 2 story brick home with internal drywall timber frame construction, I'm getting great signal strength on both 2.5 & 5ghz bands anywhere in the house and anywhere in the yard. Average lowest level around -60 dbm on both bands.
Are you in an apartment block with multiple other networks nearby? You may need to experiment with different channels to avoid interference. Give us some more information on your situation.