Hello John,
I was going to take a stab at this, but my I'm finding it a little hard to visualize your arrangement. Also, while I know the ASME Code decently well for a Chem E, I don't know anything about ISO requirements for tanks. So, I can't be of direct help, but hopefully I can point you in the direction of people who can.
1) I would make a hand sketch of the vessel you're trying to design. It doesn't have to be completely detailed or to scale, but just show the relative location of the elements you're describing in your question (at the very least show the shell, cone, and manway). If you can provide dimensions and thicknesses, add them on there as well. If you have any notes or questions, I'd put those on there and draw arrows pointing to the joints or elements in question.
2) I'd head over to the eng-tips.com Boiler and Pressure Vessel forum and try asking there. Make sure to upload your hand sketch with your post or upload somewhere else and link to it. I lurk there a lot, and there are a lot of experienced pressure vessel guys over there. I think they'd be more suited for answering this question. To make their jobs easier, I would also reference the specific ISO standard number you're building to, the specific ASME rule you've tried to apply, and any other references you've used in your calculations. That will let them know if you're looking in the right place or not. The more clear a picture you can paint up front, the less time will be spent trying to further clarify what you're asking about.
Here's a link to that forum: http://www.eng-tips....der.cfm?pid=794
Good luck.