Regarding the Galio change on pbe for Shield of Durand

Shield of Durand (W) First Cast AP ratio increased from 4% to 5% Second Cast [New Effect] now deals [20/30/40/50/60 (+20% AP)] to 60/90/120/150/180 (+60% AP)] (like damage reduction & taunt duration, this increases with charge time)

Why not make it small base damage and damage amp with the amount of hits he had taken during the duration like his old ult?

Example: 20/30/40/50/60(+20%AP) to 40/60/80/100/120 (+50%AP) + 10/15/20/25/30 (+5% AP) Per hit taken