I've limited knowledge on a lot of things including Horton's, but my Excals have scope mount parallel w/ rail. That's what I'd shoot for.

I had an older 4x Horton scope once, kindly replaced by Horton when it was out of warranty, [kudos to 'em] and could never get it 'on' at various ranges for some reason. IIRC, a friend had given me a used Excal Vixen to sell for him and the scope was on it.

I was 'spoiled' by then w/ the Excal Vari-zones which make that sort of problem go away 'toot sweet', by adjusting poi from 250 - 350 fps from 20-50 yds.

If you don't have a broom w/ 1" diam handle, a slightly smaller one will work if you wedge the top of inside rings to the stick.

edited to add: sending pm