Do you know if adjusting the hex screw that contacts the switch plate is okay to do?
I get the black char mark on both the switch plate and the screw head, wouldn't this indicate it is too short and there isn't enough contact?...and that loosening the screw slightly would lengthen the piece enough for better contact...
The one in the center? Absolutely don't mess with that at all after the heater has been fired the first time. There are two ceramic washers on the screw (you can see the outside one) that keep the screw centered and isolated by sitting in wells in the base piece. Then there's a tiny nut you can't reach from the outside that would otherwise spin (lucky for us as the 'washer stack' has to stay stacked tight). Then, and here's the really bad part for this idea, the heater lead threads onto the screw for 3 turns which jams the nut but it also fuses to the SS screw threads when heated and the metal structure changes making the heater wire stronger but more brittle. Once fired up, you have to rip the heater out to get to the screw stub and nut (meaning a new heater element of course.
And, of course, the heater has been fired a dozen times or more by the time you get it between building the core and assembling/testing the total unit.
This is what that 'custom fitting' is about. Different thickness shims (actually different thickness outer ceramic washers I think in the end?) move the screw tip in and out but must be correct before the heater is fired (or even fitted for practical purposes). Adjustments here call for new heaters (having ripped the original out by the root, literally).
IMO this is (attaching the heater to the screw) is the hardest part of LL cores, second to fitting the heater in the cores in EO (which I'm not to be trusted on, mine don't stay well centered in use). Feeling the threading of the heater lead onto that tiny screw down in the cavity in the screw base those 3 full turns is the key skill. The spiral of the lead is slightly undersize of course but opens up as you thread so it will go on if well centered and not forced......however, backing off causes the spiral to tighten and grip the threads like grim death. Even without heating you usually can't back it off past the first turn or so, yanking it out and trying again is the only recourse. If you're not very careful with the end (start of threads) you're SOL big time.
Definitely leave that screw in the center alone. If you turn it, it won't unthread (the nut will spin with the screw) but the heater will stick to the screw at the bottom and you will pull it out of line if it doesn't break all together. It won't change that length but will make a big old mess.
Sorry for the long answer, but hey, you asked.....now you know as much as me?
OF