PIP mandat recon - wait for copy of assess report?

Hi. I have questions regarding whether to wait for a copy of a PIP assessment report before submitting a mandatory reconsideration request.
My son has suffered from fibromyalgia/ CFS since 2012. He was also diagnosed with chronic anxiety in 2017. He recently had a PIP re-assessment, which reduced his total 2016 award from 15 points for daily living and 12 for moving around to 0 and 4 points respectively. The decision-maker’s letter makes us think that the assessor did not appreciate the severity of his condition, from her evaluation of his demeanour. The letter also includes one wholly inaccurate statement.
We are going to request a mandatory reconsideration and we are prepared to go to tribunal with representation if necessary. We have only just realised that we are entitled to see the assessor’s report. I have requested it today, and have been told it should arrive in 7-10 days.
Having the report would enable me to present better arguments in my mandatory reconsideration letter. But we have only 13 days left before the deadline for submitting the mandatory reconsideration request.
If the assessment report doesn’t arrive in time, I will obviously submit the reconsideration request anyway. But I still have the following questions:
- In general, how important is it to present detailed arguments when requesting a mandatory reconsideration request?
- We want to move this forward as soon as we can. Should we just submit the request now?
- I understand we are allowed to present additional medical information within a month after submitting the reconsideration request. Are we also allowed to submit more detailed arguments within that one-month period, without additional medical information? And how relevant is it to provide detailed arguments – does it even get considered by the decision-maker carrying out the mandatory reconsideration?
Many thanks in advance.

I agree with Gordon ( and he knows far more than most) make the MR as detailed and 'watertight' as you can.

Gordon,
By the way, thanks for highlighting tribunal wait times, hadn't realised they were so long.
To answer your last point - we spoke to a solicitor who specialises in this area, and he recommended not to make the reconsideration submission too lengthy, because he had found very long submissions often don't get the attention they deserve. Although he wasn't prescriptive, we got the impression he thought 2-4 pages might be best.
Do his comments on lengthy submissions fit with your own experience?
Do you have a view on a sensible min/ max length?

Peter