Tips for radial wheel truing
It's (a lot) harder to achieve in-out motion than side-to-side, and generally requires (much) more that 1/2 turn adjustments.  Plus you must usually loosen spokes on either side (2-4 spokes away) of a high spot, or tighten spoken on either side of a low spot.  For low spots sometimes you need to tighten ALL the spokes except those over the spot.

But at some point you need to either scrap the rim or employ a tool to bend the rim.  Bending out low spots can be effectively handled with a jury-rigged tool consisting of a couple of blocks of wood with holes drilled in them and a piece of "all thread" with a couple of nuts and washers.  (I've never dealt with high spots serious enough to require the opposite tool.)