Venerable Bhante Yuttadhammo,
I found more material on vikkhepo and avikkhepo under Visuddhimagga XIV,
139, and Tiika, samaadhi.
Tiika: <Avikkhepo sampayuttaana.m dhammaana.m avikkhittataa.
It is non-distraction, because it causes the accompanying dhammas to be
undisturbed.

Yena sampayuttaa avikkhittaa honti, so dhammo avikkhepoti.
By which the accompanying dhammas are non-distracted, that dhamma is
non-distracted.

Avuupasamalakkha.nassa vikkhepassa pa.tipakkhataaya cittassa
upasamanaakaarena paccupati.t.thatiiti upasamapaccupa.t.thaano.
It is manifested by way of peace of the citta that has the characteristic of
peace and is opposed to agitation. >
With respect,
Nina.