Dynamically positioning a signature in iText

After much tinkering, I've been able to find a way to dynamically populate a signature image to the bottom of a PDF as follows:

            PdfReader reader = new PdfReader(...);

            PdfStamper stp = PdfStamper.createSignature(reader, os, '\0'); 

            PdfSignatureAppearance sap = stp.getSignatureAppearance();
            sap.setCrypto(key, chain, null, PdfSignatureAppearance.SELF_SIGNED);
            sap.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED);
                
            
            Image image = Image.getInstance(imageBytes);
            sap.setRender(PdfSignatureAppearance.SignatureRenderGraphicAndDescription);
            sap.setSignatureGraphic(image);
            sap.setAcro6Layers(true);
            sap.setImage(null);
            
            int page = reader.getNumberOfPages();

            Rectangle pageSize = reader.getPageSize(page);

            int verticalPosition = (int)(pageSize.getBottom() + 70);
            int signatureEnd = (int) verticalPosition + 50;
            position = new Rectangle(50, verticalPosition, 250, signatureEnd);                        
            
            sap.setVisibleSignature(position, page, null);