This is expected, as components attach just like they would using mark attachment (and thus not contribute to the advance width of the base glyph).
Use #entry and #exit anchors instead:
(Also, using the “entry” and “exit” names instead of a generic “connect” allows you to chain components. For example, add both an #entry and #exit anchor to _smart.n-second-stroke and now you can create an m from a stem and two consecutive acres.)