preview-scale-function in the
preview-appearance group controls this. From the customization menu:
Preview Scale Function: [Value Menu] preview-scale-from-face
Calculate preview scale from ‘preview-reference-face’.
This calculates the scale of EPS images from a document assumed to have a default font size given by function ‘preview-document-pt’ so that they match the reference face in height.
Scale factor for included previews.
This can be either a function to calculate the scale, or a fixed number.
Try setting the value to various fixed numbers. The preview sizes should shift up or down accordingly.
In order to see the rendered LaTeX equations scaled
#+BEGIN_SRC emacs-lisp (setq org-format-latex-options (plist-put org-format-latex-options :scale 1.4)) #+END_SRC
The scale 1.4 is Ok in my setup... try it, and change the number to fit your needs.