Understanding EPC & heating differences

bordercars

we had an EPC performed on a flat, and got a rating of C 76 points. Same build ground floor units range from a score of 60 to 76.  our aim is to be social responsible landlords and our current rents are between 60 and 75% of the going rate, Affordability therefore to upgrade is going to be hard so we need any help we can get.
I can understand variance in panel / oil filled and night storage but no things like immersion heaters .
We have an elderly single gent 'B' who through ill health is feeling the cold ( inside temp measured at 82 ) 
We have been told assistance from ECO4 might be possible but the C rating is stopping an application. 
My question really is the old NSH are not past their best, do we remove and supply panel or oil rads and get the EPC done again or just add more of something and bite the bullet on costs for both 'B' and ourselves. 
Image shows units 5 and 10 the two with the biggest variables. 

matt_drummer

So you want to know what you can change to make the epc worse so that it is low enough for somebody other than you to fund the upgrades to the properties you let?

Or have I misunderstood your question?