I put a new 800 MHz directional Yagi antenna up about 25 feet today. I get the control channel full scale but still not picking up anything. Guess the Uniden BCD536HP doesn't do simulcast.
BCD536HP will decode multicast rather well, you just need an antenna that isn't a whip/omni. Preferably a yagi tuned to the 850-900mhz spectrum and aimed as the primary tower site that you're wishing to receive and decode from.
If you're getting a strong signal from the said tower, and it's not having issues keeping locked to said control frequency... then it's likely the system isn't being utilized currently. For example, JoCo MARRS simulcast sometimes goes dead silent for up to 15 minutes - not a single key-up anywhere - and this system is traditionally extremely active.
For example, when atmospheric ducting is ongoing, I can sometimes decode KSICS Leavenworth County KS rather nicely here in south JoCo KS - well outside of the coverage area. Just because you may be in the red circle as listed on RR's site, doesn't mean you'll always get a strong signal from X-named site. P25 has the same signal fade that analog has - further you get from a site, the weaker the transmission becomes. Hence why trunking became a thing with a multi-site system to bat that issue right out of the field. KSICS, however, tends to be "one tower per county", whereas localized county (or regional/metro) installations are multi-tower simulcast systems (MARRS, etc).