Thanks guys, looks like macros are blocked by their server. I managed to find another way around the size issue.

One thing that helped us and found by chance is that while an image is merged in a table cell as is, when merged into a Text Box, the image can be manipulated to some extent by sizing the text box to only show the parts of the merged image that you want. In our case the image had to include a specific ratio for it to be sized correctly, so we create the image with the correct ratio then use the Text Box size to crop the extra white space that we don't need shown in the final PDf.

This may help someone else that is battling with merged images in table cells or help them to come up with another idea with this info.

Thanks again!