Last I read they will adjust fixed tariffs to match the
2.5k cap as announced recently by gov. However that could vary by the company, I'd presume they all fall in line as its also a nice deal for these companies overall, less bad debt etc. Oil is included, otherwise that would be discriminatory as you cant help where you live and everyone is paying the same tax which is the ultimate source for how gov can take these actions.
Add in the 400 discount and it equates to +6% over your current cost pro rata