Comment 1 for bug 1170239

J -
Here is a partial solution the issue.
For the ocular module, you can manually edit the ocular.ini file and enter the more exact mag factor:

[lens]
0\name=My Lens
0\multipler=0.63
1\name=My Lens
1\multipler=0.6

The second digit shows up in the on-screen description, and is used in the displayed FoV ( you can check this by comparing it to the single digit example 1\)