I think I can see where the confusion lies, related to the nomenclature.
The C rating DOES NOT change when run in parallel, consistent with what I initially believed. However, because it’s expressed as a cumulative sum of storage capacity (which I neglected to consider), which has doubled, in this case because it’s still 10C, it’s expressed at the 20ah, rather then the 10.
My concern was everything I’ve read says you need more 100At o get going. Based on this, you should be right. Hope this helps someone else.
(where’s the wiki??!)