we do similar . i have 1 rope attached to the front of the boat and then a second rope attached mid way down the port side both these ropes are attached by a stainles carabina to the rope for the sea anchor. plus a slack line attached to the narrow end of the anchor for easy retrieval. lots of rope but still fits nicely in the one bag to keep it all tidy and out of the way. using long ropes we drift pretty much sideways and keeping ropes out of the way of any lines, been doing this for years and never had a prob. the sea anchor sits aprox 40 feet from the boat so well out of the way. 

 I just use the one rope attached to the bow Jack, then use the motor to square the boat up , i have another tie off point about a third of the way from the bow if the boat refuses to sit right.  Also have a slack rope tied through the anchor so you can pull it inside out for an easy retrieve , works just as well tied around the outside so your not lifting a bag of water. Always drive the boat up to the anchor for retrieval anyay.

How I use my sea anchor depends on what conditions I'm deploying it in, there's no hard and fast positions to attach it to on the boat. If it's relatively calm I'll use two ropes tying one off the bow cleat and the other off the stern cleat and run both out about 10 - 15 metres

Heavy weather/large swell, single rope of the bow cleat and with anything up 20 metres of rope.

If there is not much of a drift but I just want to slow the boat down slightly I'll use a quite short length of rope from the bow and stern cleats, 5 - 6 metres tops.

 I must be doing it wrong. I tie it off the back of the boat and Y it off the stern cleats or lader handles. High freeboard and swim platform at the stern of the Caribbean so never get any water coming over.