To use your Mixture and Radiator keys you first have to hit the buttons for AUTOMATIC MIXTURE and AUTOMATIC RADIATOR keys.

Thats the way to disable the automodus ingame.
Or you can just disable the automatic modes in the difficult-settings.

Exactly - if you want to govern the mix and rads yourself, why click the automatic boxes in the settings?

it is rather counter intuitive. And I only discovered the affect by accident. Particularly since I re-mapped most of the keys and did not think I needed anything that said automatic.

Binding the radiator and mix axis seems a bit flaky. I bound radiators +/- to the throttle hat switch on my X52 and couldn't enter cockpit view till I re-installed completely....

I put the radiators on the two spin wheels below the MFD on the X52Pro throttle, and they work great. It does take a significant amount of spinning them to manipulate the rads, but it's a pretty great setup at this point in my opinion. Makes it very easy to know which is which as well, water radiator on the left and oil radiator on the right which is the same as the in-cockpit lever setup. Should be the same with the La5 as well since it's the same airframe with the Ash 82 engine instead. There's so many knobs and levers on the X52 Pro that can be utilized as switches and key presses it's amazing. Everything located below the throttle's MFD can be mapped, which adds quite a bit.