In short, if the waveform is too small and you can't see where a sound ends and where another starts, there's a simple solution: enlarge it!
It's a well hidden feature, but it's there. If you move the mouse at the bottom of the waveform, the pointer will turn into a sizing tool and you'll be able to enlarge and reduce the audio waveform dragging up and down.
And while we're at this, remember that the dot key on the numeric keypad allows to play back only the audio, in real time. No need for time consuming previews.