well yes it matters to an extent......i have found the measurements where my bullets meet the lands on almost all of my guns, but seating the bullet close to them doesnt always equal an accurate load. In fact I have one particular rifle that likes the bullet .090 off the lands (which is not concidered close by any means) however I always start close when testing .... (.015-.030) and work out from there. Another thing to take into concideration is cycling through your magazine, it wont do any good to have a bullet seated way out, but not function through your magazine! Some guns (300 RUM etc.) you need to find out how long it can be to cycle through the mag and then work from there.