170 is a pretty high temp for your chicken breast. I typically don’t cook them past 160 or they will get dry very quickly. When finishing on the grill I smoke them to 155 and check them on the grill with my instant read thermometer. You are right about the thighs, they are much more forgiving. You can safely cook the thighs to 165-170 and they will be moist. I insert the probe into the thickest part of the largest thigh and cook to temp. rather than time. I imagine the time listed in the guide is based on the size of the chicken parts. Enjoy and have a good cook.