It seems that from yourn description you are referring to the Truma system and not the ALDE system as no elements are exposed as water is heated in a jacket and the ALDE has a safety cut out to prepvent such an issue arising. However if you can show I am incorrect I am happy to learn as I am only going on what ALDE told me. Howecer always best to cautious.
See their page 7 , giving sectional view:
LINK
Here observe the cylinder holding the "green" fluid, this is the ethylene glycol inhibited fluid[
"antifreeze"] the subject of the OPs level concern. {the other green items shown are electronic bits, not part of the antifreeze]
In that toroidal void, so within the green fluid are two electrical elements, here shown in red. You should also note that not only in the green fluid but their upper connection is very high up within the fluid, so particularly critical to being in any "air" space, should the boiler not be fully filled as required. This also applies to their seals in the bulkhead connections, all 4, so these will be particularly prone to abuse from overheating.
Also observe the inner cylinder, this is the alloy gas burner can, here a grey colour. its crown by definition is at the top so very prone to gross abuse if fired up with less than a fully filled antifreeze toroid.
For completeness the water section is here shown in blue, this toroid lays outside of the antifreeze cylinder so any heating here is only heat transferred directly from the antifreeze's cylinder. In that it is not exposed to any greater temperatures than the antifreeze , nor does it house any heating item, element, can etc so why whether that is fully filled or empty is is of no matter from a damage point of view.