Thus the voltage is reduced by the leakage through the set grass and weeds. But the feet and nose of both sheep and sheep predators are also wet at this time so their total resistance is also reduced. One thousand volts may be enough for this situation. At 5 p.m. the grass is dry, and so are the animals' hooves and hair. Thus the animals' resistance to electrical flow has increased considerably, and more voltage is needed to open the door for energy to flow.
Energizers also vary.
Some deliver higher energy levels at lower voltages to an animal than other energizers. So the guidelines are just that - guidelines, but not scripture. So, when you read voltage, the total situation must be taken into account before concluding which is good versus not good. One needs to take several readings in order to observe a trend, and the readings are not always transferrable between energizers. Animals react differently to an electrical shock.