It is important to understand the timeline for the application of these markings.
The plan to mark allied aircraft with identification stripes was given in 'Operation Memorandum No 23 Distinctive Marking-Aircraft'. This was issued by SHAEF on April 18th 1944. It was 'Top Secret' and therefore not widely circulated. It was to be more widely distributed a few days prior to the invasion.
SHAEF ordered units to start applying the markings on June 3rd in preparation for the scheduled invasion on June 5th. This was obviously a bit of a rush,compounded by the heavy rain on June 4th which,as well as leading to a postponement of the invasion until June 6th,also washed the markings off many aircraft. One US unit sought special permission to send a party off base (they were locked down) to seek more paint locally!
The standard of application on these aircraft immiediately prior to D-Day varied greatly,some units would have been more careful than others. However aircraft arriving at squadrons after the invasion would have had the markings,or partial markings,again depending on the date,applied at a Maintenance Unit. You can bet your house that these would be properly and neatly applied.
Remember also that a rough edge on a full sized aircraft amounts to a very small variation on a scale model and is very easily overdone.