Great question! I talked abit more bout adaptations and responding to stimulus on this topic:
I would say it depends on the rider when they respond to a stimulus but by week 6 of the plan they will have gone through 2 cycles of work:rest so there will definitely be some gains, the reason we put HM there is to avoid the plateau by shifting the stimulus to keep you working towards the targets.
Mentally, it can also be really beneficial to do the ramp mid-way and see some small gains as this will help keep your motivation going all the way to the end of the 12 weeks and leave you wanting to build even more 