It is better to plan and do things properly. Things might turn out fine by hoping for the best and doing a bodge job some of the time but not 100%. Things are fair less complicated when done properly in the long run. You are never going to get solid consistent results by estimating measurements of OA.
The amount of times when doing a spot of renovation I come to find half washed paint brushes and unwashed paint trays..it makes the next job harder having to replace brushes and trays. If a few extra minutes were spent doing the job properly there would be no complication and no wasted time nipping to the shops (or to the hospital if you apply the example to OA vaping).