Argh, I just found this :
"1) If the damage is within 1" to 2" of the edge of a door, fender, hood, quarter panel, trunk, or roof, PDR probably will not work 100%. These areas contain "double metal," which limits air space and tool accessibility to completely remove the damage." http://www.dingsplus.com/paintlessdentremoval.htm
When I checked the dent, it felt like 'double metal'.
Paintless dent removal may not work in my case then. sigh.