What kind of spiders are you tying Jon?
Is it the hackle profile that's not quite sitting in the suggested position?
If your hackles are lying flat down the hook, and as you say, not sticking out, perhaps you are overlapping the turns of hackle with each subsequent turn, winding the hackle from the eye of the hook, down the shank towards the bend????
If this is not the case then please accept my apologies, but if this might be the case, make sure you tie the hackle on with the outside facing towards the eye, and this will take advantage of the natural curve of the feather to replicate the parachute/umbrella profile of the hackle. And start your hackle another millimetre away from the hook eye, and make your turns in front of each other towards the eye, so as the stalk of the feather goes around the hook it sits tight against the stalk from the last turn, in front, but not overlapping, or squashing it, as this forces the hackle down along the shank of the hook. You should only be doing two turns of hackle max anyway for spiders. A turn and a half is enough.
Another thing ... which end of the hackle feather are you tying in? Is it the thick end of the stalk, or are you tying in by the tip of the feather? Tying in from the tip means the stalk on the feather is at it's thinnest, as it tapers from a thick bulky stalk down to almost nothing at the point. Tying in the thickest part of the stalk creates bulk at the head which you end up covering with more thread than you would like to and more often that not this bulky head now needs to be tightened down against the hackle which flattens it.
Your hackles should be soft, for spider patterns. You want them naturally folding back along the hook in the water. You say you are using a black cock cape, I would be using a hen cape Jon.
Regards length of hackle, there is a cut off point, but some people have success fishing short hackled spiders, whilst others tie there's slightly overlapping the bend. It's probably more important to tie your spiders sparse and not overdress them.
PM me you address and what spider patterns you want to tie, and if I get your PM in the next few hours I'll post some lovely hen hackles just right for the job. You should have them by Monday and that will give you the week to get some fleas tied up at night. As you say the cock fibres are stiffer than hen (even if soft) Do you have partridge feathers? You shouldn't be without partridge n orange, partridge & gold style spiders. So simple to tie, so deadly. I'll send you some partridge as well.