Prior to the most recent TBS version, which includes Optimised Runway Delivery (i.e. an indicator is presented to Director which is threshold wake separation + expected compression), then the wake separation was delivered to 4DME. so a 4nm H-H separation minima was applied when the leader got to 4DME, with compression reducing that as the leader reduced speed. There was no wake separation applied once leader got to 4DME. Tower would give the caution at 0.5nm compression.
With current TBS we separate to threshold.