Here is a small patch that add a new setter and getter "preferedSignatureSize" to the SignatureOptions. So the user can set the approximate signature size on one's own.
We use a small amount of bytes for the signature itself like 0x500 and additional calculate the size of the whole certificate chain that should be wrote inside the signature. This is much better than setting a fix signature size.
If the user don't set any size, 0x2500 will be reserved.