If the ambient temp will work for the snake, that's fine. Where would the temp need to rest in order to get make that a healthy situation for the animal? I'm imagining that 90+ is a little too warm.
I've never done it but I would assume like any setup it depends on several other factors. But I agree that 90+ would be to high. If 88-90 is considered warm and 80-82 cool I would think somewhere between 84-87. But like I said I'm not all to familiar with it.