FAR 61.160 references bachelors and associates degrees specifically, no mention of masters.
But the FAA institutional authority list DOES list one master's program at ERAU... I'd check with Riddle for clarification.
It would make sense from the FAA perspective that a two-year master should provide the same R-ATP as an associates, if the flight training part is the same. But the issue is probably more on the academic accreditation side... how do you get masters-level accreditation for something that's inherently vo-tech? Kind of like getting a masters degree in welding. Maybe you just have to take a lot of extra classes to get to the post-grad level.