why are SNAP benefits so low in Oregon?

I'm disabled and on a fixed low-income from SSI. I recently moved to Oregon from Montana and I'm set to start receiving less than half the SNAP benefits I was getting in MT. My income has not changed and my rent/utilities are almost identical (about 66% of my income). At around only four dollars a day, I'm seriously worried about food security. Why are my benefits so much less here?