They normally favour, Science, Physics, Chemistry, Maths and English from what i have been told in the past.
Only one requires good spelling and gramour, otherwise i would have failed Maths and Physics.
The ATPL Theory is a combination of English, Maths and Physics more or less, so asking for those A-Levels could show that you are of lower risk to fail the material. Ontop of that, having done an A-Level, the workload compared to GCSE's is 3 or 4 times greater, so if you can cope with A-Level then i guess you could more than cope with the ATPL's.
However, most people i have met, pilots, wannabes, student pilots, dont have A-Levels. But all i have met on a sponsored course, have had them, i guess they need to filter out applications some way, and why shouldnt people be rewarded for staying in or going back into education.
As for making your results better, do it for yourself, as i dont think sponsors and FTO's really care, as long as they are above a C that is.