If you take cos45º(14.5") you get 10.25".
And if you take (10.25"/11)inv cos you get 21.28ºThat gives a mouth of 12.5" x 25".
Using 11" as the top and bottom with 3/4" wood and 12" x 24" mouth, the depth is 11.09", that´s close enough, so this is how I´ll build them.
I´ll begin cutting wood on monday.
Regards
Kim