4w3s are much more outwardly and "other" directed in the way they carry themselves, while 4w5s go inward.

Think of it this way, there's the core 4 fixation of envy and ruing over shame from abandonment. Then the wing is what they "do" with that fixation. So the 4w3 will take that envy and shame and create thie external persona that seeks validation of the image.

Just imagine blending 4 and 3 energies, vs 4 and 5 energies.

Enneagram 3s are "other directed" and seek to conform to an ideal image that others have deemed worthy and aggressively pursue living out this image. They have what Claudio Naranjo calls, a "marketing orientation" - picture those salesmen that try to promote hard enough at you so that you'll buy what they have. This is what the enneagram 3 does in the way it seeks to "sell" it's image to people, thus the "assertive" disposition.

So 4w3s are 4s that have the influence of what I just described with the 3 and the focus on outward presentation and other-directed images.

With 4w5s, there's the influence of the withdrawn 5 tendency to detach and go inward, to observe things, and be hesitant to actively engage.