Distance Enquiry gives different result in OTM vs Carrier

We are using the default OTM functionality of doing the distance inquiry between two locations and the results fetched are showing different results. We have not made any modifications to it.

Rate Service ID	Rate Distance ID	OTM Distance	Carrier Distance
Rate Service ID	XYZ	Rate Distance ID	HERE_LAT_LONG	OTM Distance	1,450.03MI	Carrier Distance	1668 MI
Rate Service ID	XYZ	Rate Distance ID	HERE_RATE _DISTANCE	OTM Distance	1,450.03MI	Carrier Distance	1668 MI
Rate Service ID	XYZ	Rate Distance ID	LOOKUP ELSE ESTIMATE	OTM Distance	1,740.04MI	Carrier Distance	1668 MI
Rate Service ID	XYZ	Rate Distance ID	ESTIMATE	OTM Distance	1,740.04MI	Carrier Distance	1668 MI

Postal Code: 61761 to 78439

What can be the potential reason for this gap? Any suggestions in this regard, would be highly appreciated.