Most commercial barbecue sauce is made with sugar and tomatoes. Both of these items burn at very low temperatures. Allow the temperature to drop significantly before adding barbecue sauce to the meat. I can hear it now . . . . There are several options to consider.
Many salad dressings make excellent marinades.
We would also thin these in the same manner. Play around with different ideas and see what fits your palate. Soon, and with some practice, you will learn the answers to these questions. Two factors are in your favor, for adjusting for the proper amount of heat . . . . . On charcoal grills, there is normally an adjustable cooking grid that may be lowered closer to the heat.