When you say the "13mm pad" are you referring to the weld shoulder? l like your bussbar material with no slots, but I think I would prefer drilling a 6mm hole and mating to the flat 10mm pad as intended by the mfg.I bought a 2mm flat bar of 99% pure copper on Amazon $17.99. I cut it to length to cross both terminals and then drilled 10mm holes so it is tight against the 10mm post and sits flat on the 13mm pad. I then used a washer and nut to tighten it down so I get contact with the 13mm pad, the 10mm post and the washer and nut on the post. I do not think you can get anymore contact then with this method and the copper conducts electric at a much higher efficiency.
Amazon.com: 2pcs 99% Copper T2 Cu Metal Flat Bar Plate 2mm x 12mm x 250mm : Industrial & Scientificwww.amazon.com