i've always feed autos exactly like i feed photos -- soilless context.
They gow and develop in the exact same ways in similar rates of growth etc etcc. auoflowers are not different except for their trigger to go into flower.
fertilizer instructions, especially marijuana brands, consistently tell you to give WAY too much be default. This is what causes the false idea that autoflowers are somehow magically and drastically different. This is an outcome of majority of people overfeeding their plant and one that goes into flower sooner is going to exagerrate the effects of doing so.
if you are dealing with mostly an inert substrate at thsi point, 40-60ppm of P and 180-200ppm of K is going to be enough for 90% of plants. If you have amendments in your soil providing some p and k, that needs to be considered in addition to what is added in the fertilization.
P and K rely significantly on "active transport." Some does enter through diffusion but there are feedback loops in the plant that makes the intake of P/K more on demand than relying on random diffusion across root membranes. You only have to ensure the 'right' amount is present around the roots... concentrations where it is easily 'grabbed' and transported inside the plant by carrier proteins and also not so high that it interferes with other nutes around the roots.
Provision of nutes is not about the ratio of how they are used in the plant. they are about a ratio and concentration that is conducive to being readily available around the roots. This sounds like it is the same thing but it is not.
Relative to autoflowers and photoperiods the components of stems, leaves, cellulose, thca et al are still the same. They are not constructed differently. It's the same formulas, the same building instructions in the DNA. The differences between these genetical compatiable plants is almost non-existent outside of how it enters flower phase. if everything is built the same and they grow in similar ways, then the inputs are going to be the same too...
in soilless/hydro stick between 1.2-1.5EC ... possibly more with some genotypes and maybe slightly different ratio due to oddball genetics, but the differences will be easily mitigated through observation and slight adjustments to the formula provided. the more whak-a-doo the formula is, the more deviation you may see... imbalanced formulas will manufacture problems and inconsistencies that are easily avoided otherwise.