30PG/70VG or 30VG/70PG ?

If 70VG, try use fewer/looser cotton, maybe it's thick juice so your wick couldn't keep up with the chain vaping, my guess?

Thicker wire or bigger coil diameter reduces the chance of getting burn. Bigger diameter enables you to put more cotton.

Spaced coil also has less chance of burns due to less compressed heat.

TristanX was right. Larger diameter and more cotton can solve your issue [but dont put too tight]. I use 3mm diameter and thicker wire on my Topbox nano. No more run dry issue like last time i was using 2.5mm diameter.....if puff more it will run dry easy and got burn smell.
Running @ 0.73ohm @ 21w on a single coil with 3mm diameter coil......good.

Tighter cotton or looser cotton has no correlation to the size of the coil.

It simply refers to the amount of resistance you feel when pulling the cotton wick through the coil.

If your cotton is too tight, it restricts the juice wicking thru the cotton, so you get burns. A looser cotton wick will allow easier and faster flow of juice, so it won't burn so easily.

A 70%VG juice is quite thick (when compared to a 50/50 juice), so the wick has to be a bit looser than your current build in order for the juice to flow fast enough to avoid burnt hits.

Just use a bit less cotton than what you would normally use; you'll have to experiment to see how much cotton suits the juice viscosity in that particular build. Also if your atomizer has juice flow control, open up the juice holes a bit more.