The ideal solution is to use a thermostat with multistage capabilities that would only bring on the extra banks of heat strips as needed. The 1st 10KW could be brought on by one contactor through W1, the 2nd 10KW contactor brought on by W2.
If a multistage thermostat isn't practical time delays or outdoor thermostats could be used to control when the 2nd bank of heat is activated.
Another strategy with heat pumps involves setting up one 10KW bank of heat connected to W1 of the thermostat and the other 10KW bank being activated by the defrost board of the heat pump. If the heat pump can't keep up the thermostat will call for 10KW heat, when the heat pump goes into defrost the other 10KW will come on. Once the heat pump catches up electric heat is dropped. A simple wiring change achieves this, no additional parts required.
Im not disagreeing with a word you just said. Your obviously more knowledgable on the subject than me. I was commenting on a earlier post in the thread were someone said they always change seq. with contactors when theirs a problem. I wouldnt thank thats a good idea especially when you suspect ambient heat is preventing the seq. from opening.