ideal A-form RNA Helix

The tutorial (https://nbviewer.org/github/RosettaCommons/PyRosetta.notebooks/blob/master/notebooks/14.00-RNA-Basics.ipynb) claims that using:

assembler = core.import_pose.RNA_HelixAssembler()
helix_pose = assembler.build_init_pose('ggggggg','ccccccc')

should generate an ideal A-form RNA helix. However, the longest the sequence the closer the base pairs are coming together and a non relasitc helix is produced (see rna.png).

Am I missing something to get an ideal A-form RNA helix?