You said diff ÷ shares × 100 = luck
So by your logic I'm at 6,743% luck which seems pretty damn excessive but on par with my shit luck in anything else in life.
All ratios are PART / WHOLE so in mining PART = shares and WHOLE = network difficulty
(SHARES/NETWORKdiff)*100 is your diff rating
(456,170,867,212/30,977,000,000,000)=1.4%