IMHO the coriolis effect caused by the increased coning angle is an insignificantly small component of the rrpm rise.
The main one is the increased angle of attack (resulting from increased air flow up through the disc). The angle between the relative airflow and the total reaction (total rotor thrust if you like) remains roughly constant for a given set of conditions - it represents the lift:drag ratio of the aerofoil. So if the angle of the relative airflow increases, this tilts the total reaction further forward (ie in the direction of blade travel) and this pulls the rotor blade along harder - ie the rrpm increases.
The converse is that in the hover, you are flying in a descending column of air - ie air is going down through the disc and that tilts the total reaction backwards, tending to reduce rrpm unless you have lots of power on!
EC