actually, to be 100% sure the chain is not overtightened it is best to do it with the front sprocket, swingarm axle and rear sprocket are in line. As that is when the distance between front and rear sprocket is largest and hence the chains is stretched most.
If there is just a very little bit of play remaining on the chain the tension is perfect.

On bikes with long suspension this usually translates to a lot more play on the chain when the bike is on centre or side stand than people are used to from sports or naked bikes.