avoid that figure gets its own page

I didn't have had success with the \topfraction, but there is another important setting which gave me less float-only pages. With \renewcommand{\floatpagefraction}{.8}% I was able to specify that only pages with more than 80% of floats, will become pure float-only pages. The default is 0.6 so if a figure consumes 60% of the page it will get its own float-page.

HTH math.

Default for LaTeX is to allow up to 70% of the top of a page to be float (set by \topfraction as .7); up to 30% of the bottom of the page (set by \bottomfraction as .3) and at least 20% text (set by \textfraction as .2). Perhaps increase \topfraction using \renewcommand{\topfraction}{.75} as a start.

For more on TeX's float algorithm, read How to influence the position of float environments like figure and table in LaTeX?.

I had the exact same problem and I fixed it by setting the [ht] options for the figure environment.