In various applications of RFID systems a reader should reliably get the ID of the tags that are within a bounded proximity region, termed the interrogation zone. This gives rise to two types of errors 1) False Negative Detections (FNDs), when tags within the intended interrogation zone cannot be read and 2) False Positive Detections (FPDs), when tags outside the zone can be read. The detuning effect experienced from the object a tag is attached to exacerbates the occurrence of FND. Solving FNDs by increasing the reader power increase the probability of FPDs for tags outside the zone. Hence, the design of an interrogation zone poses a trade-off between readability inside versus outside the desired zone. We present a novel method to reduce the probability of FNDs and FPDs, and practically equalize the achievable range for tags experiencing detuning. We propose to impose intentional interference on the communication between reader and tag. The expected effects of the proposed method are evaluated using experimental measurements. The results are positive, showing a sharp edge of the interrogation zone, and a strong equalization of the range of tuned and detuned tags. Hence it is concluded that by imposing interference enables design of well-defined interrogation zones for passive RFID systems.