The resonance positions are determined by the natural frequencies of the system, which are in turn determined by the physical properties of the system. For example, in the case of a vibrating string, the natural frequencies are determined by the length, tension, and mass per unit length of the string. If any of these physical properties are changed, the natural frequencies will also change, and hence the resonance positions will change.
In the case of a tuning fork, the natural frequency is determined by the length and thickness of the prongs. If a tuning fork of different frequency is used, the length and/or thickness of the prongs will be different, and hence the natural frequency will be different. This will cause the resonance positions to change.