Performance (number of transactions) and domain size

Hi,

I'm currently doing a load test on a domain that spans to 6 different machines.
With just a little change from the earlier version of the system, i found that
the number of transactions / seconds in the current version drops significantly
compared to the previous version. The previous version uses 1 machine only
within the domain, and each transaction could involve up to 6 machines.

There are of course other differences between the two versions, such as weblogic
server version, java version etc., but just out of curiousity, i wonder, does
number of machines effect greatly in terms of number of transactions? I'd assume
there would be some latency caused by communication between machines eg. when
one server uses connection pool targeted to a server in another machine etc., am
i right and how significant is it?