The issue here appears to be the usage of the word 反映. Since you seem to be familiar with the core meaning of the word, let's look at the structures this word occurs in. It has several "patterns", if you will. First, let's look at what dictionaries have to say: デジタル大辞泉（小学館）
２ 対照的に色がうつり合って美しさを増すこと。「壁と床 (ゆか) の色が面白く―し合っている」
The first two senses obviously are more literal and closely related to words that talk about physical phenomena like 反射. Our focus is the third one, the figurative usage of 反映.
This 反映 chiefly has these patterns that you will likely encounter:
- 1 Aを/はBに反映する
- 1a Cが/はAをBに反映する
- 1b AをBに反映するC
- 2 Aが/はBに反映される
- 2a Aが反映されるB
- 3 Aを/はBに反映させる
- 4 Bが/はAを反映する
- 4a Aを反映するB
Here apparently we are dealing with 1, more specifically, 1b. How the actual sentence is best rendered in English depends on context and style. に doesn't always have to become "in", but "in" is a good place to start. I am going to give you a couple more examples before we move on to your sentence at issue.
趣旨(A)を素案(B)に反映した意見(C) (source: 西宮市 official website)
(literally) Opinions that reflect the main point(s) in the draft
(Or in other words) Suggestions that allow the main points to be reflected in the draft; suggestions that show the main points reflected in the draft
レンタル傘の利用情報(A)をＳＮＳ(B)に反映するシステム(C) (特許庁 registered patent JP2012008614A)
System for incorporating usage information of rental umbrella into SNS (official translation)
These highly reliable power generators have been optimized for plasma loads with a design that reflects our many years of knowledge that includes power generator applications. (official translation)
I understand where your confusion is coming from. When you try to render a sentence following this structure in a different language, B and C both seem to do the "reflecting" or at least both seem capable of reflecting A. But as you can see from the examples, C always has more of an active role than B in causing or allowing the reflection of A.
real wages that reflect price fluctuations in/in terms of/in the manner of/as indicated by wage growth
By the way, I disagree with the other answer. Pretty sure this に is a 格助詞.