I agree about the Excess Reportable Income date and am relieved to say I have been doing it correctly. I always buy distributing ETFs outside tax shelters which means the the amount of excess reportable income is usually peanuts, but clearly this would not be the case for an accumulating fund. So in my example for SWDA, income could be avoided by selling before the end of June (period end 30 June) and swapping to HSBC's HMWO*, then selling HMWO before its July ex-div date and buying back into SWDA. Doing what I originally said and selling/buying either side of the distribution date would not have worked.
The 30 day rule provides scope over what capital gain/loss gets booked. If someone did not want a gain or loss that tax year, simply sell HWMO and buy back SWDA within 30 days. The capital gain/loss on HWMO should then be very close to the loss/gain on SWDA.
Regarding the FX rate to apply, I always use the one on the date of the distribution. I have never really thought about this though, it just seemed obvious to me that this is what I should use. Be good to find a definitive answer - there are many things that seem obvious when it comes to tax rules that are wrong!
Regarding this:
Must admit that I thought it was proportioned, such that if you held for say 3 months in total across a reportable year you should declare 25% of the excess reportable amount as having been 'received' on the distribution date.
You are probably thinking about the way bonds work. You are liable for tax on interest accruing on a bond between payment dates. Usually this is clear because most bonds trade "clean" and the interest accrued is on the deal ticket. However, you are still liable for tax on interest if the bond trades dirty. You have to work out what this interest is yourself, which can be a bit of a nightmare.
*Vanguard's VEVE could be used instead, but a small amount of excess reportable income would arise because VEVE's accounting period is also at the end of June.