A lot of people stress about this leading up to their first big wall, having the idea they need a tight belay point at all times (“What if I fall out of bed?”), but once on the wall people tend to be so knackered, and so happy for a flat spot to flake out, as long as they’re tied somewhere then they tend to feel grand!
As you said I tend to have a loop or rope end running from the belay down to my side of the ledge and then tie into this (an end rather than a bite of rope is tidier). By tying in you’re removing a link in the chain, krabs and slings, and I always tie in with a figure-eight having once untied (I think) myself when sleeping! Tying in also gives less clutter at the tie in point which can make it easier to sleep (I’ll also often remove my daisy chains, fifi if I can for the same reason). Another option is to clip both ends of your daisy chain into a knot in the rope using back to back lockers which creates less bulk at your waist when forced to use a bite of rope. This thing about removing bulk and clutter at your belay point when sleeping for more than a night or two is that such clutter tends to make sleeping harder, something always jamming under your body or snagging on your bag (I also take off leg loops if I can).
Rope length is adjusted so as to give me enough slack to move around where I need to get to, lay down etc, then fine-tune the length with a Grigri or jumar (in a big storm you should remain as tight as is manageable as ledges can be ‘tumble’ easily, one good thing about enclosed ledges being they keep you all together!)
When using a storm fly it is possible to clip into the bear paw if you really have to, but just make sure each part is secured by a screwgate or maillon (connection between paw and fly plate and belay). If you’re using a ledge that features only webbing (Fish, A5, Metolius, old BD ledges) then the tie in point is NOT full strength (Some ‘belay loops’ are only designed for stoves or head torches!). For these types of ledges, or for the BD design if you want redundancy, trail a rope end in under the fly, or through the bottom of the zipper or drawcord tube (for enclosed flys). Clip into the rope end via your daisy chains (not into your harness as it will soak up water, while your daisy chains will absorb less) then clip some gear into the rope outside to create a loop lower than the bed. This way gravity will make it harder for water to move along the rope to your safe haven (you will always be wet in a storm but there’s a difference between damp and warm and soaking and shivering.
One thing I always emphasize is never to be complacent, no matter how big the ledge. If falling off will be the end of you then tie-in to something as you never know what might knock you off, from rocks or people to blasts of wind that turn empty portaledges into killer kites. As on all walls, take death seriously and don’t die from hubris.