prosper, minipage, space above figure

[Rochat E]

Good morning
I inserted 2 minipages on a slide (based on the prosper class). The left 
minipage has text, the right one has a figure with text underneath.
Unfortunately, there is a big gap above the figure, which I would like to 
reduce. I cannot use the options of floats (it doesn't seem to be possible to 
insert a float  within minipage). What can I do?
Thanks for your help
Etienne Rochat