Could it perhaps mean that I need to apply the gelcoat a little more thickly, as I'm usually concious of not spraying too much and creating sags or uneveness that might affect the appearance of the cured fabric. 

If this is a risk then perhaps I'd be better off just using the Aerofix 3 for help in positioning. I know the debate's been had in other posts already, but I've found it doesn't leave any residue, even without using an in-mould coating, just so long as you finely mist it   from distance onto the fabric and allow it a little time to settle before positioning.. Early attempts spraying direct to tbe mould caused problems and when i'd gone a bit heavy with it in places. .