How exactly does the ilvl sync in Frontlines work?

[Ultimatecalibur]

You seem to be slightly confusing what is happening in 2.

The only gear that gets stat boosts in PvP is gear with Morale on it, and in that case the piece's stats get a bonus equal to the difference between the stat's cap at the boosted ilevel and the cap at the items base ilevel.

ilevel sync works by capping the maximum benefit gained from items to that of the chosen ilevel's stat caps for that slot's pieces. The lower secondary stats on items above i150 are not getting boosted; they are just not being capped prior to i190. Beginning at i190, both the higher and lower secondary stats on non-pink gear is higher than the i150 caps.

The i150 secondary stat caps for each slot are

1H Weapons: Det 39(?)/Piety ??/All Others 40
2H Weapons: Det 53/Piety 46(?)/All Others 56
Shields: Det 14(?)/Piety ??/All Others 16
Head/Hands/Feet: Det 30/Piety 26/All Others 32
Body/Legs: Det 49/Piety 43/All Others 52
Waist/Accessories: Det 23/Piety 20/All Others 24

caps with (?) by them are unverified because there is no i150 piece with that as a high secondary.