I agree with the fact that a healthy bettas should always be able to breed. I personally always feed my planned breeders a bit more 1-2 weeks ahead for the actual spawning process. I prefer using live food (red mosquito, artemia and white mosquito), but also feed granulat and frozen foods. This way they can build up just a little more reserve which may come in handy in this energy-costing process.
Many greetings from the Netherlands,
Joep