Both questions are sort of general and apply to all printers.
1st, each printer manufacturer builds their printers with no linearization in place. I would have to assume this is because each customer will use different inks and print on different papers so whatever they put in as linearization would not benefit you or would now not be 100% accurate. I assume it's expected that if you want exact linearization, that you are to do that yourself based on your inks you buy, and your substrate you print to.
2nd, you will want to change these outputs to something less than what they should be once printed, (e.g.) make the 90 and 80), but what that actual number is, really depends on the actual results printed on the shirt. You would get that with a densitomitor. Most people don't buy these but they are good tools. Sometimes, you can locate a local offset film house and they will have one and can read your films for you for a small fee (if not for free).
You typically can get "very close" by adjusting a little with the assumption that you will typically have at least 20% gain in the shadows. If your printer is a high rez printer like 1200 or higher, then your highlight dots can be more well defined.
Some people will want to beef up their small dots so that they hold them easier in the screen but be aware that you need to stay away from putting 1 in the 0 range as that puts 1% dots in what should be white outside your art. Even be careful of putting 2 in the 1 range. Simply for the reason that if you have to double hit something, it will make that area too heavy, and what is intended to be soft fades to nothing will all of a sudden become too abrupt and noticeable at the end.
If this RIP has a preview of the ripped file, then you can make an your first adjustment, (save that) and then make another adjustment (save that also) and toggle back and fourth between the two previews to see what one makes more sense. Use a grayscale ramp from 1-100% to check this with because you will be able to see abrupt jumps or light spots easier this way.