Hi, Amy-
I'd have to see you driving to really be able to comment, I think...I go a lot by what I see happening with the tug loop support straps(do they show a slight 'slackness, 'seeable' as observer or driver), or, what I can see as I sit behind the horse as the driver. I do think Leia is on the right track; if simply because the shaft is less likely to "bounce" all the way up to 'sproing' off the top of the tug loop, then back down to 'hit' the bottom, and so on and so on, if the shaft essentially can be gotten to 'mostly' just sort of 'touch' the bottom, basically. One of the reasons I'm VERY pleased w/ my Flyer is that with a bit of initial tweaking(it has a car seat slider set up, which can be moved a bit over an inch at a time, setting-wise-so there's a way to change it very slightly, or quite a bit), I've got it to where the shafts float SO nicely, even over pretty uneven terrain or at speed (I've been using it mostly with my Handy, and have been doing more 'intervals' at the lope/gallop(sorry, my background is WESTERN, and I'm GOING to say 'lope',not 'canter'!!
, and some increasingly tight circles at same(sort of 'finding our limits', you might say!), and even then, I am seeing almost no 'bounce', nor any 'hitting' the top of the tug loops so as to 'jerk' upward on the girth...I'd rather try to adjust the seat so that I wouldn't have to consciously shift my weight(which believe me, is CONSIDERABLY more than Leia's and a point to be considered, IMO, when she talks about weight-shifting, is that she is VERY lightweight, and what works for her might not work the same for us older and'or not-so-wraithlike sorts <winks!>--to affect the balance! Heck, it is hard enough to remember that I DO have a possibly considerable effect on the weight being placed onto the horse's BACK via the tug loops if I lean forward or bend over for some reason(my whip holder is on the dash; I prefer it on the rt. armrest or seat support, but in the Flyer, that wasn't feasible...but having it on the dash means I do have to slightly lean forward to place it or take it out...of course, it is in my hand when I am actually driving, so not a very big deal...even so, I just don't want to have to 'think' about having to 'sit forward, or back'...I want to basically find my comfortable position, and then only sort of 'do what comes naturally' as I drive along...I probably am not explaining this too well; hope you get my point, though!
I DO like the open tugs w/ the holddown strap better all the time, after years of using wrap straps on an 'everyday' basis (because my Smuckers Lite came with them, and what did I know, back then??), and Tilbury tugs for the show ring(on my Lutkes, and on the advice of others). I do still use a Smuckers Lite as my everyday harness w/ my Frontier...knowing how not to overtighten the wrapstraps, I am able to essentially get even those straight shafts to essentially float in the tug loops: there IS a bit more bounce with them than with the Flyer, but not excessive,and the horses seem to remain comfortable all the while.
My only 'tweaking' of any of my carts is that I removed the lovely but heavy oak dash w/ 'heavy' rein rail off the Flyer, replaced it for everyday use w/ a couple of lightweight strips of poplar,and mounted the whip holder to those. I like Kathy's idea of the 'slip-on' dash cover, though, and could probably do something like that for mine...I have a small leather bag that I use as a spares bag when needed, but I don't keep it on the cart all the time.
Margo