This may be idiotic, but do the same modifiers that effect SO's effect LD checks like shooting further targets?
There's a difference between leadership modifiers and
command check modifiers.
Command check modifiers are:
+1 if any enemy vessels are on SO
-1 if vessel checking has blast markers in contact
These only apply to command checks, including BFI (rules page 12).
Everything else (e.g. radiation bursts, mark of slaanesh, ...) applys to command checks and other leadership tests in the same way.
There is also a special set of leadership modifiers for disengaging (rules page 33).
Do novas have to test for ld the same way?
Yes if there is a closer target within its range (i.e. closer but at least 30cm away).