Actually, IIRC, Russia's belligerant belief that Japan was weak and would yield everything if pushed was a result of a few colonial hardliners getting the ear of the notoriously malleable NII. Cooler heads, while not recognising Japan's true potential (nobody did, not even Britain), did realise that Korea was a trifle, comparatively speaking, and giving it to the Japanese was an acceptable price for their non-interference north of the Yalu: I don't think a line o the Yalu is so very implausible. Japan was being used as a proxy against Russia's grand designs in China by Britain, so such an agreement would keep diplomacy rather hotter in the Far East. In OTL, the definative closing of that question in 1905, which more or less lasted until 1931, turned attention back to Europe and helped reconcile us and Russia. Ho-hum...