Fees was the first thing I thought, but no, I checked, not part of the calculation
tbf the money I had in vanguard in those funds has been there and like that over a year where as ii was invested last month, could be something to do with accumulation as you mentioned
Is it not just that you're up 8-15% on the money that's been there over a year and down 2% on the money that's been there after a month? See the price chart.
Fees was the first thing I thought, but no, I checked, not part of the calculation
tbf the money I had in vanguard in those funds has been there and like that over a year where as ii was invested last month, could be something to do with accumulation as you mentioned
here is a comparison between the two