You know I just realized something. Saber and Berserker get power boosts from the Cultural Sphere thing just by being in Japan due to recognition of their legends their and by being closer to the place their legend took place. o,o
It's actually not a power boost, but rather summoning the hero closer to its original power in life. For example Achilles would only have his chariot as a Rider but since in Apocrypha he was summoned in Europe where he has decent fame even outside of Greece, he gets his spear and comet noble phantasms.
A person who gets an actual boost from being in a culture sphere would be vlad because of his Demonic Defender of the State skill.
A Greece summoned Heracles would be a ridiculous monster with loads of super powerful noble phantasms on top of God hand, since he is being summoned closer to his original potential.
George Washington summoned in America would still have really bad stats and stuff since that's his original potential.