Sen2Cor and coastal regions

I hope this place is appropriate to ask that question

in article from the last period –[Data Service Platform for Sentinel-2 Surface Reflectance and Value-Added Products: System Use and Examples]( its say that ““Atmospherically-corrected bottom-of-atmosphere (BoA) Sentinel-2 data are produced using the Sen2Cor processor (currently version 2.2.1), developed by ESA to perform atmospheric, terrain, and cirrus correction of top-of-atmosphere Level-1C input data [17]. The processor is considered a prototype and not validated for water and coastal regions””

My question is what is meant by coastal regions -how What is the range from the sea that the atmosphere correction wil not work good?

Thank you for the help