Crowfoot set, with enough of an extension that you can hold the extension to keep it plumb, is as good as you'll get. If your techniques under normal circumstances are good (and yes, there is a technique) then you'll be within a couple percent.
I will quibble with setting angle, however. When possible, I've usually gone with 180 degrees (open toward the handle), with just an extra nudge past the click. (We have Snap On dial wrenches) Never had an issue with that method -- and by the way, we use "Cat Come" thread gloop on EVERYTHING so we can get it apart next time. Permatex works just fine as well.
I'd suggest maybe you EXPERIMENT with an accessible fastener of similar size, try all three, and carefully note the rotational stop point, then re torque to see which angle comes closest to the real value you want. Remember, the ratchet head has a zillion positions.... Might not even be 90, 180, or zero. Might be 25 from zero either way.
