A casting core used in the manufacture of a cast engine component for a turbine engine, the cast engine component having a first area, a second area, a fluid passage wall separating the first area and the second area, and a connecting fluid passage extending through the fluid passage wall and interconnecting the first area and the second area. The connecting fluid passage having a turn with a radius (R). The casting core having a first core and a second core. The first core and the second core being defined by a set of geometric characteristics having a first minimum equivalent diameter (D1eqmin) of the first core and a second minimum equivalent diameter (D2eqmin) of the second core. A first flexible geometry factor (FGF1) being equal to:





(


D
⁢

1

eq
⁢
min




D
⁢

2

eq
⁢
min




)

⁢


(

R

D
⁢

2

eq
⁢
min




)

.