Hi LokiDR,
Certainly different situations can cause the value of sneak attack to vary, and your encounters may differ from the usual fights both in the campaign I run and the one I play.
An encounter with a single tough opponent tends to end in two or three rounds. The rogue often gets a sneak attack in the first round, but rarely would he get a chance to bluff and get another one, as the baddy is already dead or fleeing by round three.
An encounter with multiple wimpy creatures lets the mage get several creatures in the area of effect of his fireball, making his d6s really kick but. When the rogue gets the sneak attack, the wimp is usually unconscious after the normal attack damage, and the sneak attack is superfilous.
We also seem to have many opponents that are imune to critical hits, against which the fireball or multiple warhead magic missiles take nasty toll, but the rogue gets no sneak attack.
If your Rogue is outshining the other party members, you could change your encounters: use more creatures immune to critical hits; use creatures that can surprise the party from ambush, then run to surprise again later; or use a large gang of low CR opponents.