Toneburst, I had noticed the same issue, essentially there is not enough heat going to the pad with some of those bigger components. I was able to solder them with only a 15w iron but the key is to make sure to position your tip so that it is making good contact with the pad as well as the component leg. Make sure the tip is clean, excess solder blobs will worsen the problem. If all else fails you may need a new/"pointier" tip......I really had to work with some of those smaller pads playing with the angle of approach to ensure I was making good contact