I'll give the plants another go later tonight. Personally I didn't think that they would affect anything at all but the probes say otherwise. Once it's set back up and I've left it overnight I'll give it another check in the morning

To answer the other questions:

1) No mister. The humidity is bang on 50% with just the water in the dish
2) CHE for heat. The viv is for a (currently) small snake so there's only one in there which initially at least gave out enough heat to get the hot/cold variance with no issues. I've been advised against the mat with royals as trying to use that inside the viv can apparently create potential problems with larger bodied snakes. If the need arises I'll readdress
3) The CHE is in the "hot end" 3rd of the tank, plants were put in the other side, so no plant was under the CHE - mention this because I assume that even if the plants were reflecting heat they wouldn't be reflecting a great deal away from the substrate
4) CHE is on a habistat pulse proportional and the temp settings on that are at about 90, so once the ambient air temp hits the "hot side" probe underneath the air registers around 88

Will keep updated