PA API Search Items Result Count is low

When I do a Search Items Request with a generic keyword search like "Nike" or "Harry Potter" with no other limiting arguments passed to the API, I consistently get a total result count of 306. It seems to always be 306. I don't expect to get all the thousands of items these generic searches produce but I'd expect more than 306. I send partner_tag, partner_type, keyword, search_index=All. Does anyone else experience this? Thank you.