Early on in season three the Romulans seemed to consider the Dominion a threat even though they were still on the other side of the wormhole, as shown by their actions in the following episodes:
The Search, Part 1: loaning Starfleet a cloaking device (despite a certain clause in the treaty of Algernon) in exchange for intelligence gained about this newly discovered power,
Visionary: sending a warbird to destroy DS9 so it couldn't stop them from sealing the wormhole entrance
Improbable Cause & The Die is Cast: building a joint fleet with the Cardassians for the purpose of a sneak attack against the Dominion's rulers (this was the Tal'Shiar, the actual military was not party to this, but still).
However in season 5's A Call to Arms and most of season 6 the Dominion has come through the wormhole, gained control of the Cardassian Union, and is effectively winning against both the Federation and the Klingons (up until Sacrifice of Angels, anyway); yet the Romulans seem to have this naive "They'll stop once they conquer those guys" attitude. It took the events of In the Pale Moonlight to get them involved and that was based on a deception by Sisko and Garak.
What I'm asking is: why did the Romulan Star Empire treat the Dominion more like a threat before it came nearer their side of the galaxy than they did after?