@naitsir. Update: There are two modals that are available for Joomla: Mootools-based modal and bootstrap modal. I automatically select the modals based on the Joomla version being used. So, Joomla 2.5 would use the mootools modal, and Joomla 3+ would use the bootstrap modal. The problem is that the bootstrap version has a fixed width, and a maximum height. The mootools modal is adjustable and easy to configure.
I will have to add an option to allow you to choose the Mootools modal on Joomla 3+. That is the only way you will get to adjust the size. However, I don’t know how long Joomla will keep Mootools as part of its package.