I use a UTG riser with a TRS25 on one of my ARs. It puts the front sight at about mid window of the red dot. It's really no worse than a reap ghost ring. If he is using the dot correctly with both eyes open, he will mostly see the dot on the target, and the front sight becomes irrelevant. In fact you can completely tape over the front window of the sight, and use both eyes open and still get hits on the target. Red dots were not intended to be used like scopes where you focus through the sight. They were made to give a dot image that your brain superimposes on a target for faster hits.