I am not sure how to up your heat level (second part of your original question) without increasing your voltage. I don't think you can do that with your riva battery? Maybe there is something you can add to your juice to make it burn hotter?
LMAO
i've been trying recklessly to improve TH and heat...
before you read this ...

i
never done DIY and aint sober either.
tried something i got as a gift, a real champange brut 11% alcohol (very very nice one ) with bad results i dripped some on the wicks and gave my nova a good shake but the first 5 draws were dry after that my normal juice came back (low fruity taste) but i did get a small hint of the taste of the champange but i guess i could be the glass of champange in front of me

as my tank is already mixed with it ill just keep added "stuff" and reply back , ill try the vodka next (without drinking any ... lol)
edit > champange i used seems to reduce TH and mix the 2 flavours , quite surprising but not good to what i want > this mix was about 1 to 3 % champange to my normal juice
(i made sure there were no residues in my mouth of any kind)
edit 2 > i cleaned my vivi nova and dry burned for instant use
added 30% vodka and 70% of my gold&silver witch resulted in something that doesnt vape at all...
trew it away and tried again after cleaning just like i did before
filled my nova about 50 % full with my normal juice and added 5 drops
result> no difference with my juice ( 70PG and 30VG )
when i added more droplets of vodka the taste went bad and no increase in TH so i guess ill stop with this method and go for a APV to check if i get the higher TH ...
any comments still welcome , TIA