One additional option is not to specify a fixed height or minimum height for the modal.

i had similar issue, but the senario was the modal was to behave like a sidebar and had text input in this, and when i tried tu use the text input the modal sifted above the screen even thoufh the scroll was working if the there was some content outside the scroll view then that was not visible at all so in this removing the fixed hight of the modla helped me to make this work.

Hope this also helps someone else.