How to define decimal data type for fixtures in Cakephp2.x?

I am creating a fixture for testing in cakephp2.x. I want to define the field type as a decimal, which is straightforward. However, I want to define it specifically with DECIMAL(6,4), but cannot figure out how to set the digits.

I can't find it in the cookbook either: https://book.cakephp.org/2/en/development/testing.html

Any help would be appreciated!