support mastery grades make no sense

Seriously so tired of these senseless mastery grades that clearly are not functioning properly for people whose contributions are not kills. The values on the left are for me when I got an S- yesterday and the values on the right are when I got an A+ in the match immediately after it today (same champ, role, gamemode, runes, summoner spells, even same skin). The only areas where i flat out did worse were magic damage taken (total damage taken still lower) and kills yet I got a worse mastery grade.

Time 28:59, 39:53 KDA 1/2/2019, 0/0/21 Largest Killing Spree 1, 0 Largest Multi Kill 1, 0 Total Damage to Champions 4.8k, 8.0k Physical Damage to Champions 1.2k, 1.8k Magic Damage to Champions 3.6k, 6.2k Total Damage Dealt 17.3k. 37.8k Physical Damage Dealt 5.3k. 10.3k Magic Damage Dealt 11.8k. 26.7k True Damage Dealt 0.2k. 0.8k Total Damage to Objectives 1.4k. 6.0k Total Damage to Turrets 1.1k, 2.4k Damage Healed 19.1k, 31.1k Damage Taken 16.9k, 16.4k Physical Damage Taken 13.3k, 10.6k Magic Damage Taken 3.3k, 5.7k True Damage Taken 0.2k, 0.1k Wards Placed 12, 17 Wards Destroyed 1, 2 Gold Earned 9.0k, 11.6k Gold Spent 7.9k, 11.8k Minions Killed 18, 34 Neutral Minions Killed 0, 4

important comparisons with time factored in (eg in the A+ game i did 1.21 damage per minute for every 1 damage per minute in the S- game) Total Damage to Champions: 1.21 Total Damage Dealt: 1.58 Total Damage to Objectives: 3.11 Total Damage to Turrets: 1.58 Damage Healed: 1.18 Gold Earned: .93

I really want to know how this mastery grade is calculated because 1 kill and 2 deaths should be worth less than 0 kills and 0 deaths which means a 7% gold per minute difference is offsetting all of the other stats in my A+ game or there are items being factored in that we cannot view from the client/website.