Achieving a decent head?

[mancer62]

Recently brewed a Coopers Irish Stout (extract kit) which I was really looking forward to. I know the Guinness mix is approx 70/30 nitrogen/CO2 so decided to bottle it to see if bottling conditioning would be the answer. I made the brew with half a tin of Black Treacle 75g brown sugar and 500g of dark DME which claims to add body and help with the head.
A couple of months down the line here and to say I am disappointed would be an understatement. When I pour into glass its like cola and looks as flat as a pancake with no head. When tasting it isn't flat however and is not bad. but look-wise its very poor.
I have honestly had it looking better in past just using a kg of brown sugar. Are there any suggestions next time instead of the dark dme go flaked oats or flaked barley etc. Are these just added to an extract kit at the beginning along with the extract, sugar etc? what amount for a 5 gallon batch?
later this week I am brewing a St. Peters Creamy Stout kit 36 pints. Would u recommend this to be kegged or bottled. I know they corny and co2 wont achieve the creaminess of guinness but as long as i get a nice head i wouldnt bother too much.

 

[Sadfield]

Adding any sugars (adjunct) will be detrimental to head retention. DME shouldn't be the issue, it's more likely the treacle. Below is a comprehensive list of foam positive and negative factors, although some may be out of your control with kits. Fermentation, yeast health and packaging can have quite an influence.