No worries, it's not a silly question at all! The size of your rice cooker doesn't necessarily dictate the amount of rice you need to cook each time. Rice cookers come in different sizes to accommodate varying quantities of rice. However, you can definitely cook smaller amounts of rice in a large rice cooker if you prefer.
If you have a large rice cooker and want to cook a small amount of rice for different days, that's absolutely fine. Rice cookers are designed to work efficiently regardless of the amount of rice being cooked. You can adjust the quantity of rice and water based on your needs without any problem.
Just make sure to follow the instructions provided with your specific rice cooker model regarding rice-to-water ratios and cooking times. These instructions will help you achieve the desired results, regardless of the quantity of rice being cooked.