Edinburgh Sheriff Court has heard the space Ben McCreath fell through was 150mm.
Ron McFarlane, 46, who was a project director for the architects involved in designing Edinburgh's Princes Exchange, where the accident happened, said the policy now was not to have a gap bigger than 100mm.
Ben had run on ahead of his mum Louise McCreath. She had been at a meeting at her work as a receptionist at law firm Ledingham Chalmers at the Earl Grey Street development.
Mr McFarlane also told the court the policy was changed because of the tragic accident involving Ben.
The fatal accident inquiry has heard evidence that in buildings where children are anticipated to be present a rule applies to prevent gaps being big enough for a youngster to fall through, but the court heard this rule did not apply to Princes Exchange as it was classified as an office building.
The inquiry in front of Sheriff Mhairi Stephen, is expected to last around eight weeks.