You switched to a brand new magnesium float on a 30 yard pour. That's your first mistake, they're way too aggressive right out of the wrapper. You basically sanded the surface with it. You have to burn a mag float in on a couple smaller jobs first to knock the sharp edge off the blade. You pulled all the cream right to the top and left the aggregate exposed.

Yeah I was the same way, always tried to go light on the flux to keep things clean. Turns out I was just starving the weld. My moment was when an old timer told me to just dump it on like I was trying to bury the steel, and suddenly everything stuck. Felt like I'd been making it way harder than it needed to be for no reason.

Real user data" is just guessing with a different spreadsheet.