Greetings from Syncfusion.
Currently we don’t have support to customize the size of PlaceHolder text in AddText dialog. So, we have considered this as feature enhancement request and please find the feedback task below here.
Please cast your vote to make it count. We will prioritize the features every release based on the demands and we do not have immediate plan to implement this feature since we committed with already planned work. So, this feature will be available any of our upcoming release.
If you have any more specification/suggestions to the feature request, you can add it as a comment in the portal.