You’ve got it exactly right. Many advantages with not overlapping -only one of you ever ties, only one of you ever unties, you always know your partner’s behind you, she will always know you’re in front. When you ride into the vet check, you will run out immediately, fueling on the trail, letting the crew handle your horse. The folks who advised you to have short ties of a 1/ mile or so are dead on right, too. I know it seems counterintuitive because this is a distance endeavor, but I’ve done it many times both ways, and you’re team will be much, much faster as a unit with many short ties, versus several miles or more between ties.
When you get to the ride site, back track a mile or so on the first loop from the vet check so you and your partner recognize terrain as you finish that loop in the race - (Ah, there’s that one clearing - this is my last tie.)
It’s hugely fun. If you go do some R&T with the pony and your friend ASAP for conditioning rides (excellent interval training for the horse), you’ll both catch on to fast flying ties (and with frequent ties, you’ll see one of the obvious reasons not to use stirrups to dismount.
For your buddy, the “valet” runner fetching and delivering your horse (I’ve been both the front and the valet runner quite a bit), she can develop a feel for spotting the ground as she first sees you. If you can both do off-side mounts and dismounts, that’s very helpful. So she see you 50 yards ahead, hollers your pony’s name to warn you it’s her coming not someone else. At 30’, she’s kicked her feet free and slowed to a trot. A stride before you, she’s bailing off the off-side while you’re reaching for reins and tie rope on the left, you shout “Got her” and partner lets go of the rope and reins to run off hard as she can. If you did a flying mount, she never makes it past you ‘cause you’re so fast on the horse you’re already gone. If you stopped the pony to mount, you canter past your partner in the next 50’, ride a fast three-quarter of a mile and tie.
Now you’re ahead riding, you drink and take half a Gu and it’s time to look for a tie. This is a bit like your partner’s dismount in that you choose that tie froma distance for the visibility, horse footing, tree sturdiness, shade if needed, etc. You’ve picked your tree up there 50’ ahead, dumped your stirrups at 30’, hook reins lightly on the industrial twister tie at the saddle front, jump off at 10" with the tie rope only, 'biner to the tree, say whoa. and run away.
Really, practice the snot out tie selection, quick untying and fast hand-offs. Your partner can practice fast untying by paying attention to that tied horse she finds - analyzing the footing and any tangles on her run up, so she’s very, very fast at getting the horse off the tree and getting herself cantering down the trail.
Making those three maneuvers (ties, handoffs and unties) super fast will save you at least 20 minutes total in a 25 mile R&T which easily takes you to a 3 hour run instead of a 3:20 run.