The maximum length of Rycotes windshields (Modular or S-series) are calculated by adding the length of the mic to 5 cm (for the XLR). This will ensure that the microphone is mounted centrally within the windshield, and not poking out into the end cap (dome) as this reduces the effectiveness of the windshield. The length of the windshield is referred to by it's body length. So if you took off the end caps, that is the body. For longer microphone, extension pieces can be added. But the theory stays the same - the mic + XLR is the body length.
It is OK for a microphone that is too short to be in a windshield, just not the other way around. If in doubt, we have a search facility that will tell you what windshield fits what microphone.