[Errant]

the math indicates those particles are almost all dust.

I've seen several reports talking about this comet being older or having made enough passes that much of the smaller particles have been blown away by the solar wind. If true, the remaining particles should be larger than a 'new' comet's average dust particle size?

[Yosemitest]

I understand what you're suggesting but read Mikhail Maslov's Introducton to meteor activity forecasting

" The overwhelming majority of meteor activity outbursts is traced with the modelling very good.
Particles ejected by the comet form lengthy trails.
One of the reasons is radiation pressure force, which acts parallel with gravitational force.
The latter is dependent on a particle mass,
i.e. it is proportional to the third power of particle radius.
The outcrying radiation pressuse is defined by the second power of particle radius.
So far the influence of radiation pressure is the more the less is size of a particle.
Its action is equivalent to the diminishing of gravitational constant G.
So it increases the orbital period of particles,
and the tinier a particle is,
the more it is continuously retarded from larger particles after their ejection from the comet.
This process therefore leads to the formation of lengthy comet trails.
Meteor modelling is done through computation of orbital evolution of particles ejected by the comet
with different velocities in directions tangential to the comet trajectory at the moment of perihelion.
In the reality, of course, particles are ejected not only at the point of perihelion,
but also during several months around it.
However, comets are in perihelion part of their orbits during quite a little time comparing to their overall orbital period
and main perturbations happen around their aphelions,
so when comets are closer to the Sun
newly ejected particles are moving very close to them in a compact dust cloud.
This is the reason we can take that cloud as completely ejected at the point of perihelion,
it doesn't virtualy influence the results of computations.

Speaking of directions in which particles are ejected
we can say that, again, in the reality they are ejected far
not only in tangential directions, but in all possible ones.
However, ejection velocities
(from 0 to 100 m/s, and the overwhelming majority of real ejections - from 0 to 20 m/s)
are negligibly small comparing to the own comet velocity (from 30 to 40 km/s) near the Earth's orbit),
ejected particles have only slightly changed orbits and don't "fly away in all directions".
Radial part of ejection velocity defines only thickness of a trail,
which usually reaches several hundreds thousands kilometers.
The shape of the trail is defined by tangential part of ejection velocity.

And the last. Non-gravitational forces are often not taken into consideration in meteor calculations, as is in our case.
However, some of them, say, radiation pressure, can be considered indirectly.
As far as this kind of force works as diminishing of gravitational constant G, this is equivalent to increase of ejection velocity
which could be easily accounted in the model.
So this non-gravitational force, as many others, doesn't change the configuration of trails,
but leads to shifting of particles with different masses along them.

As spoken previously, meteor trails modelling allowed to prepare very good predictions of shower activity in the previous years.
More serious problem is prediction of outburst intensity -
how strong the maximum could be.
For such predictions, special empirical models were elaborated
(the single possible way in this case)
but as before, for their improvement, new observations are very necessary. "