I study Music at IB too (although my EE is in another subject), but nevertheless I may be able to help you:
First of all, you need to be more specific when saying "certain harmonic progressions". What type of progressions do you have in mind? Jazz improvisation would be played over jazz harmonies with 7th, 9th chords etc. Maybe you could go into these harmonies further and sort them into different forms, such as: 12 bar blues, Bossa Nova, Funk, Bebop, Ballads. If you listen to some of these forms, the improvisations are remarkably different.
So... for your research question, it could be somewhere along the lines of:
To what extent are jazz improvisations varied when played over different harmonic progressions?
Notice that I've changed 'certain' with 'different', so that it would imply that you are going analyse and compare the different harmonic progressions.
This is just another idea that you may want to consider. After all, it is your EE so your topic should be focused on and tailored to your interests and ideas for research.