Yeah when I want 225 I'll only light and add about 6-8 briquettes or enough to JUST cover the wires at the bottom of the chimney to my fuel basket. I've never added a full chimney. Sounds like with that much lit coals, you're lighting too much other coals from them throughout the cook. Try and adding only a few coals and slowly bring it up to 225 and then shut down the intakes to get it to cruise. Some drums just have a sweet spot that's hard to fight though.
I've never tried the water pan in my UDS. It works well with the ECB, but that's like a WSM and is designed as a water smoker. The UDS is not.
BUT, as Bo said.....fiind what works for you. Give it a try and see if that helps.
Big JT's Smokin' BBQ Competition Team
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