I wouldn't go crazy since sometimes all the heat from welding can actually weaken the metal. Just put a little diamond shaped piece over the affected areas to get the longest weld surface and avoid welds perpenducular with the frame. Make trapezoids, parrallelograms etc... Also the frame right there isn't nearly 1/4" I would just use 1/8". You want to match the current setting (and of course plate thickness) to the source metal so you don't burn through. I would just use 1/8, tack one edge, then use a hammer to tap the metal to follow the contours of the frame. you can also weld in 1" segments then heat and hammer the patch as you go to "stretch" the patch over the frame if it is curved.