MFG Fair Value, page-110

Just to add to what you are saying, I think the most recent Funds Under Management figure is $113 bn and the St James Place mandate was for $22 bn
so by my calculation present funds under management are probably in the vicinity of $91bn now.
ie $113 bn - $22bn = $91bn
But hey this is not all bad.
Average FUM 31 December 2019 were $92.8 bn (check here) and guess what ???
the share price was at it's highest at about $67


so where is the price now with $91bn (after SJP has left the building) .... about $21.40
ie 2/3 less than what it was worth when magellan had the same amount of funds under management in 1/1/2020
ie 70% less than when the company had the same FUM in 1/1/20
And to add to your great point...
when MFG had only $70bn in funds under management December 28, 2018 the stock price was $23.79
ie when the company had $20bn less in FUM it was worth about $2.40 more than it is today @ $21.40
$20bn is a lot of money and bizarrely that is almost equivalent to the whole St James Place mandate.
so MFG today has $20bn MORE funds under management than it did in 2018 but it is trading at 14% less than what it was in 2018
bizarre...