Since they're treated as ranged attacks, all the usual modifiers would apply. Like cover and environmental conditions.
Range is tricky, since spells don't have range bands. Using the precedent of perception tests giving a -3 dice pool penalty for things "far away" is probably a fair measure for trying to cast a LOS spell on someone who's "far away".
This depends also on the spell, some indirect direct spells, Like Fireball don't need a person as a target, but a spot (They are magical grenades, in effect).
Generally speaking, if you can "see" it, you can target it for a spell. How well you have to see it - is up for debate as its not precise.
This is all covered under Choose the Target in the spell casting section. (page 281)
But for ranged targets:
If you need to see the target, line of sight can be established
with your natural vision, including using reflective
surfaces and looking through transparent objects.
Cyber- or bioware visual enhancements that have been
paid for with Essence count as natural. Any technological
visual aid that digitizes or augments the visual input
for you (a camera, electronic binoculars, Matrix feeds,
etc.) doesn’t work—you’re looking at a generated image,
not the light from the real target. Spellcasting by visual
targeting is subject to normal visibility modifiers. You can
use visual targeting to target astral targets when you’re
in astral space (you’re not technically seeing them, but
the analogy works).
So the only modifiers that apply are visibility modifiers. (foggy? dark? too bright? etc...)
Range has nothing to do with spell casting; As long as you can see your target, you can cast at it.
Now, when you get to indirect combat spells and how they work (page 283) we get some specific details.
(bold for brief notes)
Indirect: All indirect combat spells originate near the
magician’s body (most magicians use their hands or eyes,
but some use their feet for “power kicks” or emanate
power from the entire body for a kind of an aura-throwing
effect). The spell then is launched with an Opposed
Test that pits the magician’s Spellcasting + Magic [Force]
versus the target’s Reaction + Intuition, kind of like shooting
a gun (in this case with bullets made of acid, or fire,
or something equally unpleasant to be hit by). So you
don’t really need to be able to see the target—you can
cast these spells blindfolded or with artificial image enhancement—
as long as you’ve got a clear line of fire. The
Damage Value of a successful indirect combat spell is
Force + net hits, with an AP equal to –(Force). Damage
from an indirect combat spell is resisted with Body +
Armor (adjusted for the spell’s AP). Area indirect spells
travel from the magician to the point of detonation and
then go boom. The test is like that for grenades (p. 181):
a Spellcasting + Magic [Force] (3) Test with scatter of 2D6
meters. Unlike grenades, you get to add your net hits on
this test to the Damage Value of the spell, but only if you
beat the threshold; otherwise the spell still detonates, but
the hits are used to reduce scatter by one meter per hit..
* Indirect spells are basically treated like "magic bullets"
* They need a clear line of travel from caster to target
* They don't require LOS to cast
* anything between the target and the spell will cause it to miss (such as a window)
* Range is not a factor - the spell goes until it hits.. something. (remember, even a "miss" with a spell - or a bullet! - still lands somewhere...)
* Cover would affect the outcome - in some cases
So for indirect spells like lightning bolt, or flamethrower things like cover, and blind fire would apply, (and other visibility modifiers) but not a range modifier.
While for things like fireball and ball lightning; visibility modifiers (like blind fire) would apply, but things like Cover not so much. (the magical whirling flames that fills the AOE doesn't care you are hiding behind an over turned couch...)
EDITED: been drinking, cleaned up spelling and snark.