small buffer = no clicks, large buffer = clicks?

I have just migrated from an old XP 32-bit machine to a new W7 64-bit machine. I have loaded Sonar 8.5 64-bit, and am running 64-bit versions of Dim Pro and Rapture as well. In addition, I have other 32-bit SW synthesizers, which I am running both standalone and within Sonar using jbridge. (I was running Sonar 32-bit on the previous machine.)

When operating the SW synthesizers standalone (Rapture, Korg KDLE, etc), I have to reduce the ASIO buffer to 64 (~1.5ms latency) so that the audio won't break up. If I increase the size to 128 or 256, there are clicks, and sometimes, long periods (e.g. seconds) of distortion.

Isn't this the opposite of expected behavior? I would think that a larger buffer size would result in freedom from clicks, etc.

Similarly, when running the synthesizers under Sonar, I have to increase the ASIO buffer to 128 to avoid clicks. This seems more pronounced with Rapture. Therefore, I need to change the ASIO buffer depth depending on whether I am running the synthesizers standalone or within the Sonar host (Standalone = 64, Sonar = 128).

Any idea what is going on here, and is it possible to find one ASIO buffer setting that works for standalone operation, and within a host?

thanks

Keith