Yeah, add poor glide path control to the list. I was going to suggest pilot skill (basically the same thing from a different viewpoint) but felt it was too obvious. In fact, poor glide path control isn't always pilot skill. Sometimes inadequately balanced/trimmed planes won't do what's needed. Or can't do it.

But that's gawdawful bodaceous ground effect if it's working at 1.5X the wingspan to float the model. Methinks adding better elevator effectiveness to the list of solutions would be suggested for those deadstick Q500s that are caught by that amazingly strong ground effect while none of the other pilots are. They of course proved to have used their elevators to establish a pitch that actually slows the plane in it's lowspeed end of the envelope. And their elevators had sufficient deflection to work for them. I'd suggest those Q500s that floated over the horizon at 6' altitude need some trimming. CG and elevator deflection would be worth a look.