The "battleFireSpeed" is the actual interval of the fire movement, not the numbers on the buttons (same goes for the other speed settings), so you have more precision that way. For reference, these are the fire button values:
slowest
1 -> 40ms
2 -> 30ms
3 -> 20ms
4 -> 10ms
5 -> 5ms
6 -> 1ms
fastest
So for example if you want something between the 5 and 6 settings you can set it to 2-4. No decimals though.