MB, Welcome!!
As you have found, every cook has it's own variables.
Temps, wind, (impatience

, Keep that lid closed!!

)
Sometimes we wait for what ends up to be excessive shrinkage and the ribs are over done and either dry or too tender and mushy!
One of the biggest variables is fuel moisture content. (IMHO)
Lump is not as susceptible.
Briquettes will suck up humidity like nobody's business!
The ignition speed and heat output really seem to me affected.
I've started storing 2 bags of briquettes in our air conditioned basement,
replacing and rotating one as one gets used up.
Much more reliable performance!!
-YB