Reciprocity failure is controlled by many variables and there's no guidelines that suit evrey possibility. Ilfords chart is just a starter you raelly need to do your own tests.

Reciprocity will differ in daylight and artifical light, actual light intensity and choice of format, lens and exposure. Something you shoot at f2 and 1/30th with 35mm needs 8 seconds at f64 with an LF lens same amount of light though.

It's just a case of bracketing and remebering what works best for you.

Ian