DMR fills a bulk chamber to 2 to 2.2 metres, loaded so that one square metre of floor carries roughly 900 to 1,000 kg of compost. Depth is the point. Air takes the easiest path, so a shallow patch or a wheel-compacted loader track pulls air away from the rest of the mass.
Once filled, the blower brings plenum, compost and the air above to one temperature, around 45 to 48 °C. DMR describes this levelling off as a job of four to five hours. Until it is done, no tunnel reading means much.