"And do your best to minimize the contrast of your light sources."
What does this mean?
"As well as consider polarized light sources"
Why?
Hmm. I'm not entirely clear on those points either. But maybe the honourable member Mr King is referring to the suppression of spectrals afforded by polarisation (?)
And of the first point, shooting in diffuse illumination reduces contrast to a more even spread as opposed, for instance shooting in bright sunlight where there are deep (black) shadows and intense highlights (for the most part beyond the capacity of all current slide films to record with any degree of adequacy).
To the OP: If the lab, or you, is required to
"tame excess contrast", then you are not exposing the film correctly and by association, process that follow such as printing and duplication will not be of the best standard; that is to say, slide film today cannot handle "excess contrast". The best illumination is diffuse (what I just said in the paragraph above).
With well-exposed slide film, you must give a pro-level lab explicit details of how you want the prints rendered; they are not mind-readers. If the slides show even exposure, printing is very straightforward, especially with hybrid processing.