Why must the Schluter®-DITRA-HEAT-E-HK heating cables be placed at three stud spacing?

Schluter®-Systems requires that the DITRA-HEAT-E-HK heating cables be installed at a spacing of 3 studs (3-1/2″ - 9 cm) in the DITRA-HEAT membrane for optimal floor warming. A narrower spacing may cause overheating that could lead to a fire or other damage. A wider spacing may not provide sufficient power to warm the floor in some conditions.