Created attachment 134358 [details]
notice the position of the mouse cursor and where the guide line is in the attached image, clicking and moving from that position will move the guide line

SUMMARY
 when hovering the mouse over a guide line the cursor changes while still away from the guide line and click and move will move the guide line, 
for example in a vertical guide line there is too much space to the right and left of the guide line that the cursor can move the line 
that area around the guide line changes with the zoom level as well!

STEPS TO REPRODUCE
1. view > show rulers and show guides 
2. create a guide by click and drag from the left ruler move it to the center of the image for example 
3. zoom to 500%

OBSERVED RESULT
you cannot interact with a large portion of the image because any mouse actions will move the guide line 

EXPECTED RESULT
the active guide line area around the guide line should be adjusted to a fixed number of pixels for example around the guide line instead of a percentage that changes with zoom level

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Manjaro
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.76.0
Qt Version: 5.15.2