Why her name is Hamasaki and not Hamazaki?

[*Petit*]

I thought, well I read somewhere really long ago, that it was pronounced Hamazaki in most of japan and that ayumi preferred it to be hamasaki because that's how it's pronounced in her language region. Or that it was a matter of dialect and that the default would be zaki? I really have no clue where I got this from , but I'm 100% sure Ive read it somewhwere when I just had gotten into her.