I tried switching the receivers, but get the exact same results,
By that do you mean that the same channel shows up high or the same sensor is high.
If you swap the sensors do the readings swap?
You also need to be a bit more descriptive about the sensors (type and link to data sheet) and how they are wired up (schematic). It could be you have an error or it could be that the two sensors are just that different in sensitivity. What does the data sheet say about the sensitivity?