Why does my 12L stainless mash tun hit 67°C so perfectly on the first try?

I've been trying to troubleshoot why my new BrewBOSS V2 keeps nailing the mash temperature on the first pass. The 12L stainless mash tun (BrewTech MT-12) is supposed to have a 10‑degree swing‑up period, but I'm getting a dead‑on 67 °C within five minutes and it just stays there for the whole 60‑minute rest.

I double‑checked the PID settings – set to 66.8°C, tolerance 0.3°C – and the copper kettle I use for the strike water is a 15‑liter, 5‑mm wall, which should lose a few degrees before hitting the tun. My water chemistry is also spot on: 150 ppm calcium, 30 ppm magnesium, pH 5.4 after the strike.

The only thing that might be off is the fact that I'm using a single‑stage infusion mash with 3 kg of pale malt and a 20‑minute protein rest at 55°C before stepping up. the recipe was designed for a 20‑L system, but I scaled it down and still got a surprisingly clean 5.2% ABV.

Anyone else see this kind of over‑precision with a new controller? I'm wondering if the MT‑12's insulated lid is just too good, or if I'm unintentionally over‑mixing the strike water. Any tips on dialing back the stability so I can actually practice my temperature ramping would be appreciated – or at least confirmation that I'm just lucky with this gear.

• Mash tun: BrewTech MT-12, 12L, stainless steel, insulated lid
• Controller: BrewBOSS V2, PID mode, 0.3°C tolerance
• Water: 15L copper kettle, 10 °C drop pre‑mix
• Grain bill: 3 kg pale malt, 0.5 kg crystal 40L
• Result: 5.2% ABV, 12 SRM, clean finish