Not sure of the exact final ratio but if you add 2 nice shots which if included are usually 100vg to make it 3mg then you could try 2 100pg shots instead to lower the ratio to nearer 50/50 so should then work with you coils.
freebase nic is the original which gives more of a throat hit in mtl kits.
nic salts are much smoother even though much higher nicotine so a 20mg nic salt tastes equivalent of a 3mg freebase.
so if your like me you puff away all day on 3mg i can get through at least 50ml a day. but a salt that is as smooth you will get a headrush of feel sick within 10-20 mins as salts enter your bloodstream a lot quicker.
one option if you dont mind a lower nic strength is to buy a bottle of pg, so add one 70vg nic shot to 100ml so to make it 1.5mg and then add 10ml of pg.
100ml will cost you £1.39 plus postage. one way of lowering the thickness https://vapable.com/product/propylene-glycol-1-litre/