You have to restart Hotscreen after you modify a .tscn file to refresh the changes. So your font size should be bigger next time.
The image send to LM Studio is obtain in the function get_screen_image_under_box() (line 84). You can easily modify it.
The system prompt ("You are a helpful assistant.") and settings (temperature : 0.8, max_tokens : 500) is sent with your prompt (line 117). I think this overrides the settings of LM Studio.