Quote Originally Posted by Neale View Post
It's a well-established technique, though! Look at it another way, it's less than half plate thickness and along an axis where there is little bending load, and where at least part of the channel is spanned and reinforced by the spindle mount. It keeps the spindle axis as close as possible to the Y rails to reduce leverage compared to using spacers. Probably won't matter too much for light cutting loads like foam but it seems like a good idea if you have the facilities to do it (and plenty of people have ploughed this kind of channel with a portable router, well-clamped guides, and a bit of care).
I see your point, it doesn't really need to be exact, just enough to avoid screw contact.