my only issue with that timing that you can scorch the sugar if you are using direct fire. the sugar can hydrate and sit at the bottom and get burned. thats why i try to add it while im at a rolling boil(it disolves faster and the movement helps to distribute it so it doesnt burn(even though im using an electric system).Another idea: When I add sugars for an ESB or a Saison with the brew bag, I mash without the sugar. I lift the bag, and while the liquid is draining from the bag or just after, I will add the sugar to the kettle before I put the heat back on to begin the boil. The sugar gets some time to incorporate that way without the direct heat and the possible burning involved from the direct heat. If you are adding sugar and syrup to a kettle with the heat on, make sure you are stirring.
My Blichmann Burner gets hotter than hell. They actually call it a Hellfire. I am careful about what I do considering I can get 110,000 BTUs.
I guess that with direct fire you really have to stir it in at either time???