i tend to agree with viper. nothing beats father time.
if you must then a low constant temperature and frequent aggitation as already described above can help.
but if you want a good result... be patient.
if its a really kicky menthol you are after maybe adjust the solution to 30% ii wouldn't go much higher as you loose control at too high a concentration. once you know your favourite strength and dosage you can even preblend with koolada and em to save mixing time. call it a ice stone.
then your basic solution, most are pretty much the same as the home blended variety. maybe sweetened slightly with low 0,5 or so of em and cooled with extra coolent. koolada or similar at sub 1% should get you close.
are you looking for a pure menthol or mint? i typically reblend a few commercials to get the profile i am after. as a pure menthol i still make my own from ground menthol crystals dissolved in pg at 10%
using that as a base you can edge it in any direction you choose with supporting...
the fa version is pretty decent. not sure if any vendors carry. if none can be found you can come back to me and maybe i can spare a sample 20ml or so.
i must agree. its no secret that i am totally besotted with Bella. actually still have 3 in my collection and use them all on a daily basis. real flavour machine that.
one current attie that i find delivers and seems to have missed the popularity train is the conqueror. ie duel coil postless...
would he agree if i asked him? my sham is a bit full of herself after becoming famous. haha
easy to become biased once you have befriended a few wiems.
petri is a winner. although mine lives on my paddy vape mech and is used for savouring and not tasting. any goodflavour dripper will work if you are not dedecating one or 3 to tasting. my 3 derringer are not all original. one is a clone and honestly still bang on. i just prefer the tiny chamber...
one more consideration that has not been mentioned. are you using the same coils in the same atties?
resistance effects draw dramatically, and if you recently started using a different coil that could also play a major role.