Yes there will be some light escaping, very little though.
You can use this calculator to estimate the performance and lumen collection and all that stuff.
The reflector I have with 3” focal length has the outer edge about .5” from the LED plane, so it collects a more extreme angle of light (which is what makes it very difficult to focus)
This 4” FL reflector will collect 85% of light instead of 96% like mine, which is a very small difference, and I think it’s worth it for the improvement in focusing ease.