Which tones are hardest, why, and where to start.
Polish is a stress-timed language with fixed penultimate stress and a weak functional load for f0. Several studies on Polish learners are known of, but only secondary citations were available (no original text), so the error direction is unknown.
Source: 均见 Applied Sciences 14, 6095 的引文列表（Wu 2011；Jozivik & Shi 2018；Chu et al. 2024；Chiang 2009） | Jagiellonian University, How Polish Students Develop Mandarin Pronunciation through Intensive Training
Group averages tell you where to look, not what you actually do. Two speakers of the same first language can differ a lot. The only way to know is to record yourself and compare.
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