I know of no instances where floaters have been attributed to either pilocarpine or Alphagan P. I find no references in the medical journals. Both pilocarpine and Alphagan P have been around a long time and both are used to refractive surgery non-refractive surgery purposes. I would expect that there would be something in the literature if this was a problem.
The subjective change in visual disturbance from floaters may relate to the area of the eye where light is traveling. If the floaters are located primarily in the center of the visual axis, when the pupils are small, a greater percentage of light is being affected.
For demonstration purposes, let's say that your floaters disrupt 1.0mm by 2.0mm of light entering the eye. That means that 2.0 square mm (mm2) of light is being blocked by your floaters. Remember, this is just for demonstration. I doubt you have anywhere near that level of floater blockage.
The area of a 3.0mm round pupil will be about 7.0mm2. If 2.0mm2 is being blocked, then about 28% of the light entering your eye is being blocked by your floaters.
If there is no refractive error, virtually all of the light entering the eye is appropriately focused at the retina. Think of the light entering the eye through a 3.0mm pupil as being 7 separate rays of about 1.0mm2 each. In the example above, 5 rays of light are reaching the retina and providing focused light, whereas 2 rays of light are being blocked by the floaters. With less of the light entering the eye reaching the retina, the quality of the focused images will be less.
If your pupil is 6.0mm, then the area is about 28mm2. The floaters are still the same 2.0mm2, but due to the increased size of the pupil you will now have about 7% of the light entering the eye being blocked by your floaters, rather than the 28% if your pupil is 3.0mm wide.
Now the light entering the eye through the 6.0mm pupil is 28 rays about 1.0mm2 each. Your floaters are still blocking only 2 of those rays, so 26 rays of light reach the retina and provide better vision quality.
Of course there are all sorts of variables, such as additional floaters in the periphery of the visual axis, change in depth of focus, the focus of peripheral vision, the greater importance of central vision, etc., but you get the idea. As a percentage of light disrupted, floaters disrupt less with larger pupils than with smaller pupils if the floaters are in the center of the visual axis.
I hope this helps explain what may be causing the floater phenomena you experience.