It was general practice from the 15th century onwards to include extensive donor's inscriptions in wall-paintings and shorter ones on portable icons. This has provided valuable evidence for our understanding of the art of the period, since the inscriptions frequently contain the names of the painters.
Quite apart from stylistic criteria, there is thus irrefutable evidence that the painters who undertook the mural decoration of a church usually also painted the most important icons -- that is, the ones that hung on the iconostasis.
We are therefore in a position to observe the same artist in both forms of painting. It is interesting that in some cases the donors first assigned the execution of the icons to the painter and later, when they had accumulated the money required, they commissioned the decoration of the walls of the church.