Reading the Geometry: A Mechanism for When Frozen LLM Text Helps Tabular Foundation Models

Zou Qingyun, Yingze Li, Nuo Chen


Abstract
Tabular foundation models like TabPFN and TabICL are often augmented with frozen large language model (LLM) embeddings when tables contain free-form text. Whether this helps is highly case-dependent: across 732 dataset–backbone–encoder configurations, 45.9% improve, 30.9% stay neutral, and 23.2% degrade. Using a fixed, outcome-free raw score, we define high- and low-readability strata before applying target-covariance Gaussian sampling, row–text shuffling, and pre-projection whitening. Each intervention reduces the mean gain in the high-readability stratum to near zero, whereas the paired intervention effects in the low-readability stratum remain within sampling noise. The first two interventions show that neither a Gaussian sample from the target covariance nor row-misaligned text reproduces the high-stratum gain; whitening further shows sensitivity to broad pre-projection geometry. Together, the results support a dependence on row-aligned embedding structure without isolating the covariance spectrum as its unique cause. The high-stratum Gaussian-replacement effect replicates on a second backbone. A within-dataset encoder ranking, Decision-Boundary Alignment (DBA), also shows stronger rank alignment with gain than the Massive Text Embedding Benchmark (MTEB) rank in our eight-dataset diagnostic.
Anthology ID:
2026.findings-emnlp.2028
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
43179–43194
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URL:
https://aclanthology.org/2026.findings-emnlp.2028/
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Cite (ACL):
Zou Qingyun, Yingze Li, and Nuo Chen. 2026. Reading the Geometry: A Mechanism for When Frozen LLM Text Helps Tabular Foundation Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 43179–43194, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Reading the Geometry: A Mechanism for When Frozen LLM Text Helps Tabular Foundation Models (Qingyun et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.2028.pdf