Question about TAX Declaration (Frankfurt)

Hello all, please help me about general information about TAX declaration. The question is simple.
I spend money for my job related study. In Protected content , I got back 30% of spending for books and lecture cost which are related to my job. But I receive only 11 % of the spending for books in Protected content are also related to my occupation. Protected content refund out of Protected content spending). My tax advisor explains that my tax rate between Protected content Protected content different so the refund rate are different. However, my tax classes are not changed. My earnings are little changed though it is 15% of gloss decrease due to the change of my working condition. I worked full year in Protected content 2013. Please let me know if this change can be reasonable or not. I don’t think his explanation is reasonable….

Thanks!