LaTeX and big font size

The first time I posted this an error occurred, so I am posting this again. I have a small problem with MatLab. For the labels of my figures I want to use LaTeX (nothing complicated, just Greek letters and subscripts) but the font size has to be big. Up to a font size of 24 there is no problem, but when I increase it to 30, the Greek letters shrink a lot instead of getting bigger like the other part of the text. Does anyone know a solution to this problem?

[Oleg Komarov]

I do not observe the same beahviour, please post code, MATLAB version and OS, for reference: http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer