The concern here is that PTC current protection devices as a class are among the sloppiest and slowest-responding over-current protection devices in use.
They’re entirely temperature-based, so the current that will cause a device to trip will vary significantly (and inversely) with temperature.
Per the datasheet excerpted below, the device’s notional switching current is 1.6A: this is the current flow expected to provoke a persistent change in device resistance within 10 seconds at some (unspecified) initial device temperature, presumably 25°C. Because of uncertainties in device behavior however, planning to operate significantly below that trip point during normal conditions is necessary; here a normal operating current of 800mA at most is suggested.
The device’s rated operating voltage is initially of no concern for choosing a device based on trip point; the device’s function is entirely temperature-dependent. Where it does become a question however is when the device “trips” and enters a high-temperature, high-resistance state. The device is kept in that state by the I2R power dissipation of the source voltage across the (elevated) device resistance, and as voltage increases, so does the fault-state power dissipation.
The post on thermistors here may have/point to additional useful information.