You should preferably keep it from touching. The enamel by itself will wear exposing the copper and create a short to the enclosure. All will still be fine as long as nothing else in the enclosure touches it but not the safest way to run it. Most folks want to go the other way and add a spacer. Why do you want to lower deeper? Is your load too toasty at the tip?
Yes, doubling the frequency does make the FETs run hotter for sure but I have run like this with no problems in the past. This is also why I never mentioned before as does shorten the overheat time if the device is left in the "on" state for more than normal use. Using normally with it on for only 10 seconds at a time with time in-between hits gives it sufficient time to cool down. And I also agree that this is wasting some efficiency as extra heat where you don't want it is wasted energy as far as I see it.
Yes, doubling the frequency does make the FETs run hotter for sure but I have run like this with no problems in the past. This is also why I never mentioned before as does shorten the overheat time if the device is left in the "on" state for more than normal use. Using normally with it on for only 10 seconds at a time with time in-between hits gives it sufficient time to cool down. And I also agree that this is wasting some efficiency as extra heat where you don't want it is wasted energy as far as I see it.