Text watermarking enables provenance tracing of LLM-generated text by embedding detectable signals, while multi-bit watermarking further encodes payloads such as user identities or model versions. Scaling multi-bit watermarking to large payloads is challenging as exhaustive decoding grows exponentially with payload length. Existing methods commonly address this by segmenting the payload and decoding each segment independently, but the impact of this design on decoding accuracy remains insufficiently understood. In this paper, we revisit segmentation in multi-bit watermarking and reveal a drawback of the commonly adopted paradigm: segmentation splits the available token evidence among segments, leaving fewer observations for each local decoding decision and thereby reducing decoding reliability. We theoretically characterize this accuracy–efficiency trade-off and empirically validate the claim across diverse settings. Additionally, we introduce a distribution-balanced detector to mitigate message-dependent bias. Experiments across multiple datasets and models show that our method achieves improved accuracy and robustness under editing attacks compared to existing methods. Our code is available at https://github.com/YouduLiu/SDBMW