80PG/20VG?
More PG = more throat hit
More nic = more throat hit
Like others have said with the vivi the coil is right under your lips so the vapor is hotter (it does not have a chance to cool down before entering your mouth like a bottom coil design). You may find that simply going to a bottom coil using that same juice would be ok for you.
You can try a few things to get what works best for you. Replace the 1.8Ohm coil with a 2.0-2.4Ohm coil (I forget what the vivis come in) this will help to cool the vapor off, but will produce less vapor also, on the plus side your battery might last a little longer.
You could try a bottom coil clearomizer, for example: EVOD, VapeOnly BCC, Kanger T3/MT3, again try a variety of coil heads (1.8-2.5) to perfect your vape.
Lower your PG, go for a 50/50 mix instead of the 80/20. I know my 70/30 juices give a lot more throat hit than my 50/50s. If you feel comfortable doing so you can also try lowering your nic to reduce the throat hit.