I've always found that #10 Remington caps work best on Treso cones; with RWS 1075s and Remington 11s following close behind. CCIs, whether 10s or 11s don't.
The smaller flash hole is normal and is there to reduce the flash back on ignition and help keep the fired caps from falling off he cone.
Fingers (Show Me MO smoke) McGee - AKA Man of Many Colts - Alter ego of Diabolical Ken; SASS Regulator 28564-L-TG; Rangemaster and stage writer extraordinaire; Frontiersman, Pistoleer, NRA Endowment Life, NMLRA, SAF, CCRKBA, STORM 327, SV115; Charter member, Central Ozarks Western Shooters
Cynic: A blackguard whose faulty vision see things as they are, not as they should be. Ambrose Bierce