There is a system of "Vessels" that work hand-in-hand with the meridians. They work to keep the body balanced. The internal arts and proper qigong training keep it working well. It acts as a reservior system moving excess qi and delivering extra qi to areas that need it. This is one explanation of why he may be more resistant.
It can also depend on who is delivering the strike, rub, press so forth.
Sharon, it makes a difference that you are female (yin/yang things). You may need to change your polarity in order to get the desired effect.