Lions share: When it looked doubtful that the Big 12 would get 15m in tv revenue for the tv revenue (which once added to 5m from other league shares like NCAA credits, conference title revenue, merchandising... gets 20m) the Big 12 was going to tell the top 3 raid risks (UT, OU, ATM) that they'd do a tiered deal to get them to 20 and everyone else equal. Considering projections were around 18m that was leading to projections of 20m & 14-17m for different teams. Fox came in with a big enough offer that most schools will get very close to 20m next year and the big 3 will likely surpass it even with the Big 12's pre-existing revenue sharing plan.

Additional payments:
In a gesture to the big 3 to make money not the deciding factor, the forgotten 5 offered their share of CU & NU's exit fees to get the 3 to 20m in league distributions this year. UT & OU declined, A&M accepted and will get their 20m.

Its easy to misunderstand. It took me some digging to get it right.