Thank you @Andrew_Steel, with a few adjustments that seems to have worked!
I needed to use a row filter instead of a splitter. This was the flow that got me there:
And here’s my rule for anyone interested:
And the result showing the bit that I pulled out for an example earlier:
I haven’t had an in-depth look at the table yet, but I’ll post again if I find any issues.
Cheers,
Richard