Melting point in hydrocarbons

Checking out the molecular structure and the melting points of various hydrocarbons I concluded:


1)branching increases the melting point of a hydrocarbon molecule


2)symmetry increases the melting point of a hydrocarbon molecule


* symmetry increases it way more than branching does.




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ordering in terms of melting points: 


2-methyl butane < pentane < 2,2-dimethyl propane


2-methyl butane is branched but has a bad symmetry, pentane has a good symmetry although not being branched, 2,2-dimethyl propane has a good symmetry and is branched.




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2-methyl pentane < 2,3 dimethyl butane < 2,2 dimethyl-butane < hexane


so 2-methyl pentane has a bad symmetry


2,3 dimethyl butane has a bad symmetry as well but more branched compared to 2-methyl pentane


2,2 dimethyl butane has a bad symmetry but it is more branched than the previous two.


Then hexane has the highest melting point. it is not branched at all and not symmetrical. so why does it have the highest melting point?




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I kept the text a bit long before asking the question because I wasn't sure if I understood the concept correctly. Can you please answer my question about hexane and correct me if I have some mistake in my interpretation of the whole thing?


