For one thing, these cache points are quite large, up to twice as large as regular points, so big that you couldn’t attach one to a spear say, and expect to throw the spear accurately over any distance.（point指的是矛尖）

这是托福听力材料中关于考古学的一段内容。该文对point有解释：

When we talk about a point we are referring to a piece of stone that’s worked to a sharp point, in this case probably to be attached to a spear. 

即point为打磨成尖端的石器。可能作为矛头。但网友这句话中的point 却很大，无法固定在矛杆上，因此，考古学家对这种石器的用途感到疑惑。

本句中up to修饰twice as large. 意为“大到有普通矛尖的二倍那么大”。这不是非限制性定语，而是对表语形容词large的补充说明。up为副词，和介词to合用，表示程度高达某个程度。

so big that...仍然是一个形容词短语，中心词为形容词big。仍然是对表语形容词large作补充说明。

so...that引导结构状语从句，修饰形容词。但该形容词本身并不是结果。