i got 2 and both mine is on the block side... my motor wsa rebuilt a long time ago and from the rebuild the timing went off a bit and therefore the timing mark was re adjusted. seems like that may have been the same for you, a motor rebuild
both my marks are like 3mm apart so i just put it in the middle for my motor... what you can try is adjust toiming to first mark and check motor and then use other mark and whoch ever is better idle is the one you use