Hi Allan
I use a 12" Dob
My usual sequence would be
31 Nagler, 22 Nagler, 13 Ethos, 8 Ethos
I think the 21 Ethos would be your best bet
the 17mm is too close to the 13mm
TV suggest a sequence of 8,13,21 or 6,10,17
But don't under rate Satchmo's suggestion of the 22 Nagler
I'm very happy with mine, but the 21 Ethos would be better
Happy shopping
