Triple Triad Plus Rules

Could someone help explain so I can understand why this got plus'ed?

https://gyazo.com/1ea65db26b0cbfe2b57495346af616ef

The card was played in the bottom right, adjacent to Sophia and Good King, Sophia gets plus'ed then combos the card above. But why was Sophia plus'ed in the first place?

Does it not work 3+8+7 = 18 and 3+7+7=17 ? There is no card to the right in the screenshot.

Both Sophia and Moogle have +3, but the strength of a card can't go past A i.e. 10, as such their side strenghts are both equal to A.

Yeah. Card numbers can't go past 10, even with ascension. 7+3, 8+3, A+9... all 10s as far as the game is concerned.