Cis-Trans Isomers Heat of Combustion

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> 
> Consider the 4 cis-trans isomers for the above compound. In what way
>  would the cis-trans isomers affect their heat of combustion.
> 
> 
> 


I think that if the substituents are on alternating sides of the ring, then there will be minimum steric crowding. But is there anything else that would affect their heat of combustions?


UPDATE: Here is as far as I have gotten. Now I think for the methyl group on carbon 4, either conformation would be stable. I am guessing that an axial methyl group would be more stable, because the axial position is free from all types of steric repulsion (This is just a guess). Is this correct?


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