it’s because of rolling resistance the 18” tires have more meat and the 20” have less meat which means less resistance. You can research EV tire rolling resistance on how it works.
The bottom one is a higher load tire which is heavier which isn’t needed the top one is correct. I try to stick to Costco website because they only install the correct load tires.
I have 2 12s in my truck with the stock speakers and it helped a lot but the stock speakers could be a little bit louder. The kicker 200.4 would help make them cleaner and a tad louder