I've recently cut my nic down as well from 24mg -> 12mg -> 4mg and while I'm obviously not getting the same kind of TH as I was getting at 24mg I have to say that a 3.2ohm atomizer at 5.5V still gives me a noticeable TH.
I've read a whole bunch of posts on ECF and other forums about how to increase TH and my conclusion is that nothing will ever be able to mimic the TH you get from stronger nic. I've tried all nicotine free liquids that supposedly mimic TH like
Flash from FlavorArt and all they do is provide a TB (throat burn

) which is not all that unpleasant but definitely not what you're looking for.
I've since accepted the price of lower TH at lower nic levels, but I still do what I can to improve it:
Vape around 9.5 watts -> Watts=V
2 / R
Take deeper, longer drags
Mix my liquids around 70-30PG/VG (PG doesn't mask the nicotine as much as VG)
Of all the flavorings I've mixed I find the tobacco ones are the ones that give me better TH (not sure why), Virginia in particular.
I also drip liquid into my atomizer much more frequently (i.e. every 5 or so drags I'll drop another 2 drops)