UMG, Retainer Box

There is a bTextureIsTooLarge limit in Retainer Box’s slate SReainerWidget, when the value is larger than GMaxTextureDimensions (default value 2048) will log warning!!!
Why exist this limit, and how can I modify the GMaxTextureDimensions value?
I use the retainer box in a scaleable canvas panel, and will dynamic modify the scale/size, when too large, there will render black in retainer box, how can I fix the problem? Help