Riva usually comes with low resistance atomizers - like 2.0 or 2.2 ohm? Is that what you have? Those are hotter than atomizers that are 2.8-3.2 ohms. Heat increases hit. You could try a standard resistance 2.8 to 3.2 ohm 510 threaded atomizer or Boge 510 standard resistance cartomizers (I use the cartomizers for juices I like). Later, if you lower your nic or have juices with some VG in them, you might appreciate those hotter atomizers.
New atomizers often have strong tasting/smelling primer on them. You can blow out the atomizer into a tissue. * Drip a bit of
juice on the atty (3-4 drops) let that soak in and vape it mostly off without inhaling. Blow the atty out and again and repeat from *. Then Blow out again and re-prime with juice and the primer should be mostly gone.
The juices sold by hardware companies are often 100% PG Chinese juices. 100% PG juices let through the most flavor but also the most of nicotine's TH and irritation. Go to real juice vendors and get some juices with some VG in them. 50/50 and 70PG/30VG are good ratios for atomizers. For cartomizers I get longer good performance with 80pg/20VG whichis a bit thinner than 70PG/30VG. (because VG is thicker)
You could also try 16-18mg juices, especially in thinner high PG juices that let through hit better. You won't have a nic fit - just take a couple of extra drags and it will make up the difference.