g day Bob,
the 16" is my grab n go; it sets/packs up in 4 unhurried minutes and for my 185cm is soooo convenient as zenith is at my eye height standing on the ground.
the 18" is where i, with a heights phobia, struggle cos at zenith the eyepiece is 220cm and i'm 2 steps up a ladder and stepping one foot across onto a milk crate to look into my straight thru finder. plus up n down to shift the ladder when turning in "dob's hole" and it comes up against the ladder when aligning. oh those views tho . . . they are worth it
i like your idea of a lower finder; get aligned then up the ladder and viewing with a right angle finder up there also. BUT my 8 strut system = unaligned struts so need another bracket/platform to mount it.
regards, L