What determines the stress of an adjective formed by adding "-ive" to a verb ending in "-ate"?

Some verbs ending in -ate keep their original syllable stress when you add the suffix -ive to form an adjective

e.g.,

imitate/imitative

meditate/meditative

investigate/investigative

For others, the stress moves to the antepenultimate syllable and the 'a' in -ative is reduced;

e.g.,

indicate/indicative

contemplate/contemplative

interrogate/interrogative

Is there a rule or any kind of historical reason why a word would follow one pattern or the other?