DYP-ME007Y Utrasonic Sensor

I have DYP-ME007Y Ultrasonic sensor.
The problem i have is that i get random strange measurements if i have objects below 30 cm.
eg. 23cm, 102cm,95cm (randomly).
I tried 3 different sensors but the result is the same.
I get in trouble as long as i will not know if the measurement i get is below 30 cm so to throw it away.
Please, advice me.
Thank you.