I have no use for a thumb rest in that location. Fingerstyle sounds best to me about halfway between the last fret and the bridge, i.e. above or behind a P pickup location. On a Ric, the only way I found that feels comfortable and sounds good is to remove the handrest (I use the Treble Bezel), anchor on the E string over the pickup and finger-pick right behind it. On the white '73 I have a horseshoe so it's pick only.