I write based on my experiences (20 or so small snakes and 12 permanent animals and about 100+ short term rescues.)

I have never know a 'poor' feeder to improve* this is not account for a snake maintained under poor conditions and improving the conditions usually husbandry and feeding are closely related. A snake in imperfect temps will often refuse. It is not always reciprocal however a snake in perfect conditions can still often refuse (this is what I call a poor feeder)

I have never had a small snake (under 500gm) refuse often, my experience is they will usually eat what is offered with little issues. I have not had hatchlings so every animal had arrived feeding and none stopped eating until they hit that close to 1000 gm mark. (I have had two stop feeding around the 500 gm area)

I would suggest the exact same check your temps carefully. I personally use for little snakes (under 500gm) 88ºF warm/ 78ºF cool ambient air around 80ºF give or take 3º. this is open to debate but I believe little snake do not need as much heat as larger animals (more active).

I would never suggest every animal will follow my pattern but this is what I have experienced.