Also if rope-walking, the height of the attachment point is less important, or arguably could be higher, as you shouldn't really be sitting down at all, and the chest ascender is essentially just an 'instant backup' should you need to take a rest. Granted this is a lot easier in a narrow pitch, but ideally all your weight should be alternately on your footloop or the foot ascender - and your spare hand, which does do a lot of the work for me. Two hand jammers might help, but would probably bang into each other a lot.
Ironically I find rope-access models very good for rope-walking as the attachment point is higher. I remember working in a narrow 'rift' between two buildings at Heathrow, probably about the same width as Bitch Pitch in JH, putting edging strips on cladding, and me and my mate had to climb past each other to pass up these 4m strips. He didn't like it at all due to the confined space, and it was all polished aluminium. I'd sneakily put my Pantin on, and rope-walked past him at a good speed - he nearly fainted, as he'd never seen one before. I let him have a go later and he was really impressed - but I use one regularly for long static jobs as you can stand on it and take the weight of your arse for a bit. Anyway, I'm digressing again...