Due to how the NGP calculation works we have to take the average for that from the instantaneous samples in the data.
This means we take each sampled speed point and then average them. This also means that if you have a lot of noise (variance) in your speed channel that you will have an average that may not reflect your true pace so that when the NGP calculation is done it may show the reverse of what you were expecting. Average pace is calculated normally by dividing distance by time.