It probably depends more on the cultivar than the growing
medium, and to some extent nutrition (plenty of phosphorus
promotes flowering).
With an Azoychka and a Persimmon growing side-by-side in
the same large self-watering container, sharing soil, fertilizer,
water, and sun exposure, the Azoychka will produce clusters
with a dozen or more flowers in a cluster, while the Persimmon
produces the same 3-5 buds per cluster, widely spaced around
the plant, that it did when I grew it in the ground a couple
of years ago.
On a cluster with a lot of fruit set, the fruits will be smaller
than if you only have a couple of fruits on a cluster. Total
pounds of fruit might be higher, though.
One thing that I do with containers like that is drill 1" holes
all over the bottom of it, so that roots can reach down through
it into the soil below to get extra water. I line the bottom with
grass clippings when filling it to keep the growing medium from
falling out when I move it around. If the containers are in a
garden bed, something that I do in one bed on the side of
a raspberry patch to let seedlings get better light, I simply
cut the bottom of the container out completely before
filling it. (Someone growing in containers because their
soil has disease issues probably does not want to do this.)
You may find this document useful for understanding the
fine points of container media:
http://edis.ifas.ufl.edu/CN004
(A companion volume from the same source on diagnostics
and monitoring:
http://edis.ifas.ufl.edu/CN002
)