Standard Dosbox answer: don’t use pirated versions of the game. Most rips are woefully broken. ?
You can get an official version over at GOG.com for 5,59 EUR.
I can confirm that Jagged Alliance is working 100% without any tweaks in Magic Dosbox. The mouse cursor is visible, both relative and absolute mnouse emulation modes are working flawlessly. All you need to do is add a new game profile, select JA.EXE as “Main Program”, SETSOUND.EXE as “Setup”, configure sound (SB 16 for Midi and Digital), then run the game. ?