I'm ashamed to say that I still haven't done any testing work on this, as my health has temporarily worsened if anything, in some respects. That's my excuse anyway.
If anyone should get a chance to test or do a packet capture then let me know.
I realise that I could do a packet capture with Andrews and Arnold’s ‘clueless' server, so I wouldn't have to set up a PC with the relevant software - I'm just using an iPad all the time these days. I’m not sure if a clueless capture at the ISP end as opposed to one at the local will be a fair picture, because although my firewall settings should allow everything outbound (=upstream) to pass through, it won't show the effects of the firewall’s blocking of some inbound (=downstream) traffic and I'll just have to allow for that by filtering in my head.