dewalt2013

Hello I've just brought myself a Dewalt 717XPS, One of the reasons I chose this model is because I you can cut skirting upright against the back fence. If I do a 45 degree left mitre this works fine. The only problem is I cant do it on a right 45 mitre. If I place the skirting upright against the back fence and change the base angle to 45 degree right I can't cut quite through the skirting without the saw catching on the fence or the top of the skirting. The skirting is about 120mm/ 5inches. What am I doing wrong here? Cheers Simon