But the ELR is simply the rate at which the undisturbed atmosphere's temperature varies with altitude.
The formation of cloud depends on the cooling of a parcel of air which is lifted within this atmosphere. The rate of cooling of this parcel is determined by its humidity. The buoyancy of the parcel is determined by the relationship between its density (temperature) and that of the surrounding atmosphere.
So, the DALR, SALR and ELR all come into play.
I too use the 400ft rule of thumb. Seems to work most of the time in the UK during the morning.