>Do you have any evidence of this?

I have been advisor to some people signing the deals. I would say that depending on the project in my slice of the industry at least 25-30% were outright redistributed to various stakeholders.

Confirmed. The second industry with such redistribution is oil and gas, 5-15%.

My figures are from ~2005.

Fun stories of hearing about key equipment gets caught up in Libyan customs. Weeks and weeks of meeting various officials, learning about each others families, drinking tea, etc, before 'the cost of compliance' is finally raised.