A simple fixed power 4x32 is ideal. There was a Finnish sniper Simo Haya in WW2 that refused to use a an optic on his Mauser. He said the reasons were, it made the shooter raise their head to high revealing their position, the glint of the scope, fogging and faster target acquisition with iron sights.
There's nothing wrong with iron sights but with our low power airguns it's nice having the confidence in more accurate shot placement.
Jsramsbottom.com sell the one piece Sportsmatch mount HOP18c with the cutaway design to allow easier loading of the Ace, Innova and some bolt action rifles. It's currently out of stock and might be a special order item.
I'm not sure why the forum was down, it wasn't for long and it rarely happens.