CGT reporting for part sale of accumulation fund - nominal distribution question

Are there any published examples for the part sale of a section 104 holding of an accumulation fund? With subsequent receipt of more nominal dividends and a second part sale? (Ignoring dealing fees.). Say I have 100 units which I paid £200 for, and then receive a nominal dividend (income tax paid) of £10, and a second of £20. I have a pool of allowable cost of £230? Then I sell half my units, leaving an adjusted pool of £115, not £130? In other words, does the part sale pro rata reduce the impact of the nominal dividends received so far - my part sale includes some of the nominal dividend as well as some of the unit value? I can't find a worked example for what must be a common question... any URLs gratefully received!

Hi,
Please have a look at:
CG51570 onwards for guidance on Section 104 holdings.
Thank you.