Keep in mind the recipe levels aren't exactly "lvl51". When you are lvl50, doing a "lvl51" synth was pretty damn close to making a 4 stars synth in difficulty.
1 Stars back in 2.xx were roughtly lvl55.
2 Stars were lvl70.
3 stars lvl90.
4 stars lvl110.

Synths we make when we are lvl51 result in ilvl115 items.
Synths we make at lvl57 result in ilvl139 items, which would result in a difference of ilvl of 24, when we actually raised our own level by only 6.

What was happening when we used ingenuity1/2 on lvl26 as we were lvl50? Absolutly nothing or very close to. I think that's what you are observing, Ingenuities works but with the actual "synth levels" differences it does pretty damn close to nothing.