ok - well iv'e fixed up my the chapter numbers as simple h2 tags in sigil , to avoid gettign side trcked by TOC issue
i thought the filepos did nothign but then i found the final xhtml contained a toc coded with links back to those filepos values, thus is was gettign out of step and confused as I messsed around.
so I ditched that toc completely, make the chapter number sino h2 tags & let calibre & sigil do trheir thing.
I now have workign toc in both epub & mobi.
& chapter start code like this
<div class="calibre1" id="filepos20356">
I am 99% sure the div - filepos line is now totally redundant but I will leave it there for now.
to test the h2 - margin top idea i go to .css
and add your line:
@namespace h "http://www.w3.org/1999/xhtml";
save - convert to mobi .. and ...
I reckon that kindle software insists on adding the space. when I@e not seen it it's because books had no chapter / header tags but just happened to have toc that worked
I think I will accept that the space is supposed to be there. note that I've learnt a bit about filepos & toc in the course of the afternoon, & quit while I'm ahead.
will be happy to read your feedback though