Interesting difference between 12" and 9" tonearms

So I just got my 1987 Decca Super Gold cartridge back from John Wright with a Decapod fitted and new Paratrace stylus. Modified Garrard 401 with 2 arms. (see my Virtual System). I installed it in my 9" Jelco TK-850 and it didn’t sound good. Lots of surface noise and missing inner detail. I adjusted VTA and VTF and improved it some but it hadn’t a patch on the other Decca (Garrott Bros Gold with new LC stylus and Decapod) on the 12". A little irked, I tried it in the 12" version of the same arm on the same table. Same cables and armboards. Ridiculous. Transformed. Minimal surface noise. Tons of detail. Crystal clear. Musical as all hell. In fact, I can’t stop playing album after album. Ridiculous! (Cross posted from a comment on @halcro post)