Hmm Bow Sight issue ???

[NorthernRaider]

I've been playing with the new compound bow and yes its a joy to use, so compact and portable, and the low draw weight hold bit is definitely very nice, but when I bought the bow I got with it a Fibre optic 3 point sight ( with built in spirit level !!!! ) and try as I may over the last 24 hours I found no matter what I did I could not get groups of under 1 ft diameter. I was to be honest totally baffled, I don't use a sight on the recurves. So I dug out my old solid steel T bar shaped foresight that I got with the first recurve but never used.

Two screws of some weird effing American thread and allen socket head size removed later and the fibre optic one was off and the new one installed, first five arrows later and a six inch group............

I've no explanation but simply putting on a much simpler and more basic sight and it shoots great.