Dear Daniel, 

The blur points on the funnel plot are indeed imputations.

The funnel plot explains the effect sizes depending on the sample size, and it usually appears like a triangle (studies with small samples lead to larger effect sizes). Here, you should check if the dots are distributed around similar effect sizes, or at least all on one side of 0 (eg. There is significant bias if some studies of small samples reported negative effect sizes, while others were positive, and the studies of large samples reported null effect).

Best, 

Lydia