Proprioception is essential for coordinating human movements and enhancing the performance of assistive robotic devices. Skin stretch feedback, which is used within natural proprioception mechanisms, presents a promising method for conveying proprioceptive information. To better understand the impact of interference on skin stretch perception and to provide insights into how to best balance between perception performance and the workload required for its understanding, we conducted a user study with 30 participants that evaluated the effect of two simultaneous skin stretches on the user's ability to perceive changes in skin stretch and the associated perceived workload. We observed that when participants experience simultaneous skin stretch stimuli, a masking effect occurs which deteriorates perception performance in the collocated skin stretch configurations without changing the perception of workload. These findings imply that multi-channel skin stretch designs should avoid locating modules in close proximity due to the lower sensitivity in perception.