There is no known contadiction or support of subatomic particles regarding the flat Earth theory. However, as you mentioned about the sun, I am supportive that the sun is small, but close. In such case, the energy received by the Earth is still the same. Whether nuclear fusion occur in the sun or not does not prove or disprove the sun is near and small. Regarding the fact that you would say that a small sun carrying out fusion would soon blow up and explode, and would not dissipate energy slowly there may be mechanisms that allow slow release of energy. In fact, such mechanism is under investigation by many scientists, as hydrogen is very abundant, and being able to release energy from fusion slowly means the end of energy crisis.