WTF is a Modified Minion?
Jim Minion uses a Harbor Freight Weed torch, and he calls it "lighting his cooker"
Let me get this straight-you are using a Stacker, the Vortex for the charcoal ring and cooking direct with the meat off to the side?
Are you using a kettle with daisy wheel vents or a One Touch?
I use small diameter charcoal rings with the Stacker and Cajun Bandit Conversion, so, I don't see where using the Vortex is an issue, but cooking direct with it certainly will be. You'll not get low temps using the Stacker without some sort of indirect heat deflector, be it a waterpan or pizza pan.
I've got 1/8" steel discs that I use with the 18" & 22" Stackers and Kettle Conversions.
You'll still be relatively close to the heat source cooking direct, and judging from what you said, adding the waterpan helped stabilize the temps, so, you kind of have that covered.
But what I have found is how very little intake is needed for the Cajun Bandit to run at 275* and how fickle it can be when you open the lid or adjust the bottom vents.
I use one for a chicken cooker at comps with a Rib-O-Lator and I got tired of my teammates constantly fiddling with the intake, and temps spiking - that I blocked off 2 of the intake holes with aluminum high temp duct tape and just have one opening to control and it worked wonders.
I look at it as a High Heat cooker and Reverse Sear machine. 275* is a sweet spot for it, but I also like that If needed it can crank to 450+ indirect.
Just for the hell of it I added a BBQ Guru adapter and just wire it up if I want a no hassle Low n Slow cooker.
Seriously, I use a weed torch to start all my cookers. Basically just flame the briqs or lump until the edges start to ash over and then assemble the cooker whether an Egg, Drum or WSM and Cajun Bandit and have the meat ready to go. In the case of a WSM, I'll have all the vents open until it reaches my desired temp, put the meat on and close the back 2 vents and control the intake with the vent placed in front.
The temps will drop when you put the meat on the grates, but will settle in with the one vent in @15 minutes and the vent usually rides open @50% to maintain 250-275*. That's the good thing about bullets-they are tight and dial in easy.
CB takes a little getting used to. Give the vent block a shot and see if it makes life simpler.