The size of the blocking filter imposes something like a field stop in your eyepiece, and therefore, the field of view is limited by it rather than the one inside your eyepiece, and it's always the limiting factor for any eyepiece with field stop larger than your blocking filter size.
For example, with a BF5, any eyepiece with more than 5mm field stop will yield the same true field of view, regardless of the focal length of the eyepiece.
Normally, we switch to lower power for wider field of view, but in this case, switching to lower power might not usually give wider field of view. It will only show a smaller solar disc. Of course, the image brightness will be affected, if you have smaller aperture front filter (the etalon), you will not like to go too high power (short focal length) even if the field of view is the same, for you are not limited by the exit pupil size (image brightness).
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