Using mostly Airflo scandi compact 390gr 31'. The Beulah 6/7 44'. Has I have mentioned I mostly use the underhand casting stroke. Guess I need more practice with the Beulah and a modification in my casting stoke.
Sometimes line profiles are not and more often weights are not what they supposed to be and based to Dans experience you should check its taper profile. You can compare its belly and tip thickness to your Airflo head if there is significant difference?
Weighing Spey head rear and front half is good measure. A head which rear has less than 60% of head mass is not easy to cast but "turns" bigger fly and polyleaders. A head which has more than 70% mass is very easy to Spey cast but struggle to straighten with big fly and when casting to head wind.