I hate to be the one to tell you, but searing marks don't make the meat taste any better. It may look better on the plate buy your palate will never know the difference.
That being said, if you really need to see those marks on your chicken you need to get the temp up there, at least over 400 degrees. However, if you do that you may end up with the sear marks you are desiring but have raw meat inside.
I never worry about sear marks on chicken or pork as I tend to cook them low and slow, as far as grilling goes. For beef it's a bit different depending on how you like your steaks, and what kind of cut you are cooking.
Regardless, if you like the way your chicken tasted, keep doing it that way.