Everytime i oil my chain i would turn the crank backwards because i don't have a workstand. When i do so there is a poping noise coming from my Ultegra 10s cassette. I found out that when the chain is going backwards , it will get stuck at one point of the cassette because a tooth at the next gear is wider than the others and would prevent the chain from properly engaging the teeth it is on. The chain would then pop back into place which explains those noises. This would happen to almost all gears especially the 3rd-6th gears. Only the 7-10th gears have no such problem. This would always happen in the same position .
Is this beacuse those wider teeth are to make shifting easier?

If you study cassette cogs carefully, you will see a number of "features" that aid shifting - twisted teeth, grooves, cuts, etc. It sounds like your chain is catching one of these features when you pedal it backward. It would not hurt to measure the chain to be sure that it has not elongated beyond the replacement point (1/16" elongation in 12"/24 links).