Inset stove installation

[ukcat]

Are there any stove fitters on here that can advise on  fitting of inset stoves as im not sure if my fitter is trying to pull the wool over my eyes. Basically my stove has been fitted  with a liner and cowl. I purchased a cowel (colt high top liner hanger type) as it has a good deep lip that comes well over the chimney pot. This type of cowl has a spigot which attaches to the liner with a jubilee type clip. My fitter persuaded me to use a different type of cowel as it was easier for him to fit as it sort of pushes onto the liner. I had concerns that his cowel may not give as good protection as my house is subject to quite strong winds and I was concerned  with driving rain blowing under the cowel lip. I've attached a pic to show the fittment and to me it is fairly poor and I'm sure that rain will blow through. So he says he will come back and fit the original one but he will do it without disconnecting the flue liner from the stove. So this is why I need someone with experience as to me he will struggle to fit the cowel properly without disconnecting at the stove end to allow the liner to lift up. I'm just worried that he's going to do some sort of bodge job in it but I've not got enough experiance with how it should be fitted 

Cheers in advance 

Edited October 31 by ukcat