Plotly Scatterternary三元坐标异常问题求助

我用Plotly制作土壤类型三元图，给特定区域的文本标注加背景框时，手动推导的坐标出现了异常：

• 明明设置a0为0.60，实际显示却接近0.63
• 底边的a值本该恒定不变，结果却呈下降趋势
• 顶部a值预期是0.69，实际显示接近0.79，而且还不恒定

我用正弦定理推导b、c轴的坐标（a对应Clay(%)轴，b对应Sand(%)轴，c对应Silt(%)轴），但结果完全不符合预期。

运行环境：

• Jupyter Notebook（IPython 7.31.1、JupyterLab 3.4.4）
• Plotly 5.9.0
• Windows 11

相关代码如下：

import plotly.graph_objects as go
import plotly.express as px
import pandas as pd

df = pd.DataFrame({"Clay (%)": [], "Silt (%)": [], "Sand (%)": []})
fig = go.Figure(px.scatter_ternary(df, a="Clay (%)", c="Silt (%)", b="Sand (%)"))

# Clay text_bg
a0, a1 = 0.60, 0.60      # bottom left/right vertices
da = 0.09                # change in vertical height
a2, a3 = a1+da, a0+da    # top right/left vertices
b0 = 0.26                # bottom left (eyeballed)
b1 = 0.13                # bottom right (eyeballed)
b2 = b1-da               # top right
b3 = b0-da               # top left
c0 = 0.10                # bottom left (eyeballed)
c1 = 0.24                # bottom right (eyeballed)
c2 = c1-da               # top right
c3 = c0-da               # top left
fig.add_trace(
    go.Scatterternary(a=[a0, a1, a2, a3, a0],
                      b=[b0, b1, b2, b3, b0],
                      c=[c0, c1, c2, c3, c0],
                      mode='lines',
                      line=dict(width=1.5, color='black'),
                      showlegend=False,
                      fill='toself',
                      fillcolor='rgba(1.0,1.0,1.0,0.5)')
)

fig.show()

请问这是什么原因导致的？

内容的提问来源于stack exchange，提问作者eigenVector5