Cognitive radio mobile ad hoc networks (CogMANETs) allow secondary users to switch channels when a primary user appears, but this changes communication characteristics like bandwidth and round-trip time. TCP CRAHN was proposed to help TCP adaptively update its congestion window in response. This paper evaluates TCP CRAHN when bandwidth and round-trip time drastically change, and then proposes TCP CoBA to further improve throughput. TCP CoBA additionally considers available buffer space at relay nodes when updating the congestion window after a channel switch. Simulations show TCP CoBA can improve throughput by up to 200% compared to TCP CRAHN.