I just post this here since I used some time to figure out (the obvious)
Instead of trying to set the criteria on a collection more 'complicated', I found that it can easily be done with plone.api, even on 'create':
my_collection = plone.api.content.create(
type='Collection',
container=portal,
id='items-collection',
title='My Items',
layout='somelayout',
query = [{'i': 'portal_type', 'o': 'plone.app.querystring.operation.selection.any', 'v': ['my_type']}]
)