🚀 go-pugleaf

Why can't you just create the formulae in FrameMaker?

I wouldn't even attempt what you are trying to do.

I usually try to be technically helpful, but in the case of filters I'll make an exception and suggest that you cut your losses. Every word processor filter I've ever tried in my entire life has been 100% absolute Crap with a capital C. And that's before you even start to think about equations, which are always problematic.

The fact that your filter is translating a formula as a table and can't even correctly map a simple ASCII character to itself (in the lower area of the character set) only proves my point.
The fact that you are using an interim (RTF) format only doubles the problem - now you have two filters and would have to trace which one is causing the problem. If you solve that one, believe me, you'll find another. (And as far as I know, RTF doesn't even have an equation capability.)

If you really really really depend on importing formulae from elsewhere then I'd try to find a way to turn them into a picture and import the picture into FM. But my suggestion is to avoid the problem entirely and enter the equations directly into Frame.