From Gabriel Zucman's The Hidden Wealth of Nations: The Scourge of Tax Havens, descriptive info at amazon:

In The Hidden Wealth of Nations, Zucman offers an inventive and sophisticated approach to quantifying how big the problem is, how tax havens work and are organized, and how we can begin to approach a solution. His research reveals that tax havens are a quickly growing danger to the world economy. In the past five years, the amount of wealth in tax havens has increased over 25%—there has never been as much money held offshore as there is today. This hidden wealth accounts for at least $7.6 trillion, equivalent to 8% of the global financial assets of households. Fighting the notion that any attempts to vanquish tax havens are futile, since some countries will always offer more advantageous tax rates than others, as well the counter-argument that since the financial crisis tax havens have disappeared, Zucman shows how both sides are actually very wrong. In The Hidden Wealth of Nations he offers an ambitious agenda for reform, focused on ways in which countries can change the incentives of tax havens. Only by first understanding the enormity of the secret wealth can we begin to estimate the kind of actions that would force tax havens to give up their practices.

I recall something you posted within the past week or two that included an estimate that at least 10% of wealth is sheltered in havens.  It led me to recall this very short and very fascinating book by Zucman.  (I am unable now to locate the thread that included this statement so am placing it here for lack of a better idea on where to do so.)