A circular polarizing filter will have minimal effect at removing that kind of flare,ie. directly toward the sun.
The 5.4 lens has a narrower field of view so tailoring as long a lens hood as possible to shade the lens/filter will clean up some of that flare. Your lens and filters need to be meticulously clean as shooting this close to the sun is going to show up any issues, in particular, the quality of the glass and the ability of the lens to damp periferal light- which is what flare is.
The lower the quality of the lens, the more need for a lens hood!
Great to see distortion free images