I had no idea what to do with my 2018 for HA D3 visits. I opted to let him go alone after extensive "preflight" talk, then told him text me when the Coach would like me to go in, "I'll be 5 minutes away..". This worked out really well, the HC liked son's confidence and appreciated being willing to talk with him alone and show him around. I got the text to go in after 30m; HC repeated a few things for my benefit, and I covered a few things in case they weren't brought up. Good experience.
(edit: HC's had requested he visit and the trips had been planned for a few weeks)