Half-elves are often not "half-elves" by appearance. The elven partner can choose the appearance of his/her offspring - either having the child look mostly human or look mostly elven. See the rules governing half-elves for the difference in abilities between these two groups. Half-elves who favour their elven parent will largely associate with elves and adopt elvish culture; though they are usually not accepted as 'full elves'. Half-elves who favour their human ancestor will largely associate with humans -except they tend to be loners and wanderers (the substantially extended lifespan does cause difficulties fitting into any human settlement for any length of time).
Lyonya has the largest half-elf population and is the place where half-elves feel most at home. In Lyonya, half-elves who favour their elvish parent are especially valued as royal rangers as they have the more .... decisive... nature of humans combined with the taig sense and other talents of their elven ancestors. Individual and small numbers of half-elves can be found scattered throughout the kingdoms. Prealith has the 2nd highest number of half-elves - a few minor communities and a large number of wandering half-elves - mostly those who favour their human parent but also those who favour their elven parent but had trouble fitting in or resented their status in elvish lands.
Other races often confuse part-elves with half-elves. These people have an elven ancestor but are over half human. As a result, these part elves inherit physical features from both ancestries (neither parent is a full elf so neither parent has control over the level of 'elvishness' of the child's features). The lesser the amount of elven blood, the less noticeable or non-existent are the elven features the person will have. A character with 1/4 elven ancestry will take the statistics and abilities of a half-elf that favours their human parent though they will have noticeable elvish features. Less than that level, the character will be treated as a human in game terms, though there may be slight physical characteristics that hint at an elven ancestor.
Finally, elves had children with every human race; however, a few races are avoided - such as the Dawntreaders, Magelords, and Wanderers. Elves seem to prefer Sea Wolves and the Sea Father's Chosen.