I wouldn’t worry about the value difference too much but more the consistency. If you need 75 degrees on the edge then keep dialing up the temp until you get it.

It’s most likely only going to affect large prints at the end of the day.

Your printer will measure the bed from a single location so moving your IR sensor will vary across the bed. If your using a custom firmware I’m sure you could set this as an offset assiming your IR thermometer is accurate ;)

Heat of the bed will be the warmest point and the periphery cooler (just like your body temp)